President Donald Trump's legal team issued a fiery response Saturday ahead of opening arguments in his impeachment trial, while House Democrats laid out their case in forceful fashion, saying the president betrayed public trust with behavior that was the "worst nightmare" of the founding fathers.

The dueling filings previewed arguments both sides intend to make once Trump's impeachment trial begins in earnest Tuesday in the Senate. Their challenge will be to make a case that appeals to the 100 senators who will render the verdict and for an American public bracing for a presidential election in 10 months.

"President Donald J. Trump used his official powers to pressure a foreign government to interfere in a United States election for his personal political gain," the House prosecutors wrote, "and then attempted to cover up his scheme by obstructing Congress's investigation into his misconduct."

Trump's legal team, responding to the Senate's official summons for the trial, said the president "categorically and unequivocally" denies the charges of abuse and obstruction against him.

"This is a brazen and unlawful attempt to overturn the results of the 2016 election and interfere with the 2020 election, now just months away," the president's filing states.

Stripped of legalese and structured in plain English, the documents underscored the extent to which the impeachment proceedings are a political rather than conventional legal process.

They are the first of several filings expected in coming days as senators prepare to take their seats for the rare impeachment court.

Senators swore an oath to do "impartial justice"' as the chamber convenes to consider the two articles of impeachment approved by the House last month as Trump's presidency and legacy hangs in balance.

One Republican whose votes are closely watched, Sen. Lisa Murkowski of Alaska, acknowledged Saturday the political pressure bearing on them.

"I'm going to take my constitutional obligations very, very seriously," she told reporters from Anchorage on a call.

The House's 111-page brief outlined the prosecutors' narrative, starting from Trump's phone call with Ukraine and relying on the private and public testimony of a dozen witnesses -- ambassadors and national security officials at high levels of government -- who raised concerns about the president's actions.

The House managers wrote: "The only remaining question is whether the members of the Senate will accept and carry out the responsibility placed on them by the Framers of our Constitution and their constitutional Oaths."

The Trump team called the two articles of impeachment "a dangerous attack on the right of the American people to freely choose their president."

Trump's team encouraged lawmakers to reject "poisonous partisanship" and "vindicate the will of the American people" by rejecting both articles of impeachment approved by the House.

The Senate is still debating the ground rules of the trial, particularly the question of whether there will be new witnesses as fresh evidence emerges over Trump's Ukraine actions that led to impeachment.

New information from Lev Parnas, an indicted associate of Trump lawyer Rudy Giuliani, is being incorporated in the House case. At the same time, Senate Democrats want to call John Bolton, the former national security adviser, among other potential eyewitnesses, after the White House blocked officials from appearing in the House.

With Republicans controlling the Senate 53-47, they can set the trial rules — or any four Republicans could join with Democrats to change course.

Murkowski told reporters she wants to hear both sides of the case before deciding whether to call for new witnesses and testimony.

"I don't know what more we need until I've been given the base case," Murkowski said.

The House's impeachment managers are working through the weekend and will be at the Capitol midday Sunday to prep the case.

Trump's answer to the summons was the first salvo in what will be several rounds of opening arguments. Trump will file a more detailed legal brief on Monday, and the House will be able to respond to the Trump filing on Tuesday.

Trump's team led by White House counsel Pat Cipollone and Trump personal lawyer Jay Sekulow, is challenging the impeachment on both procedural and constitutional grounds, claiming Trump has been mistreated by House Democrats and that he did nothing wrong.

The filings came a day after Trump finalized his legal team, adding Ken Starr, the former independent counsel whose investigation into President Bill Clinton led to his impeachment, and Alan Dershowitz, a Harvard law professor emeritus who intends to make constitutional arguments.

White House attorneys and Trump's outside legal team have been debating just how political Monday's legal brief laying out the contours of Trump's defense should be.

Some in the administration have echoed warnings from Senate Majority Leader Mitch McConnell, R-Ky., that the pleadings must be sensitive to the Senate's more staid traditions and leave some of the sharper rhetoric exhibited during the House proceedings to Twitter and cable news.

One Democratic aide said Saturday that Trump's initial filing read more like a Trump campaign fundraising email than a legal document.

People close to the Trump legal team said Cipollone would deliver the president's opening argument before the Senate and that Sekulow would follow. Starr and Dershowitz would have "discrete functions" on the legal team, according to those close to the legal team, who were not authorized to discuss the strategy by name and spoke on condition of anonymity.

At issue in the impeachment case are allegations that Trump asked Ukraine to announce an investigation of Democratic political rival Joe Biden at the same time the White House withheld hundreds of nearly $400 million in aid from the former Soviet republic as it faces a hostile Russia at its border.

The Government Accountability Office said last week the administration violated federal law  by withholding the funds to Ukraine. The money was later released after Congress complained.

The House brief said, "President Trump's misconduct presents a danger to our democratic processes, our national security, and our commitment to the rule of law. He must be removed from office.

Trump's attorneys argue that the articles of impeachment are unconstitutional in and of themselves and invalid because they don't allege a crime.

Under the Constitution impeachment is a political, not a criminal process, and the president can be removed from office if found guilty of whatever lawmakers consider "high crimes and misdemeanors."

Democratic presidential candidate Bernie Sanders stepped up his pitch to women in early-voting New Hampshire on the heels of a squabble over sexism in politics with fellow progressive and 2020 rival Elizabeth Warren.

The Vermont senator delivered a brief speech Saturday at the Seacoast Women's March in Portsmouth, saying that"we are in this together."

"Men, if you think abortion rights, if you think equal pay for equal work is just a women's issue, you are dead wrong," Sanders said. "It is a human issue and the men have got to stand with the women."

Sanders did not stay to march, heading instead to the next campaign stop. His remarks at the event came a day after his campaign released two television ads in New Hampshire. The state's primary is set for Feb. 11, eight days after the Iowa caucuses lead off the nominating contests.

One of those ads, "Our Side," says that, under President Donald Trump, "women's rights are under attack."

"Bernie Sanders is on our side and always has been," a female narrator says over images of Sanders campaigning with and posing for pictures alongside large groups of supporters, most of them women. "Fighting to protect a woman's right to choose, to fully fund Planned Parenthood, make child care affordable and guarantee paid family leave and equal pay."

Sanders' efforts underscore the important role women will play in choosing the Democratic presidential nominee in the early states and beyond. But that message may be especially scrutinized given this week's feud with Warren.

In Portsmouth, Sanders said, "What the Women's March, and what we are all about, is saying that it is the women of this country who have the right to control their bodies, not politicians."

He didn't mention Warren or the flare up-with his longtime friend, a Massachusetts senator who overlaps with him  on many policy initiatives that seek to overhaul the nation's political and economic system. Warren said this past week that, during a private meeting between the two in 2018, Sanders disagreed that a woman could win the presidency — a charge he's denied.

That has raised deeper questions about societal misogyny  that female candidates have to overcome. The senators then clashed about the "he said, she said" feud during a debate last week. Warren refused to shake Sanders' hand afterward as both of them called the other "a liar."

They were in the Senate for the start of Trump's impeachment trial on Thursday and said they'd not subsequently spoken about the inciden t. Since then, both have declined to comment further about it.

Sanders told voters at a later New Hampshire stop, "I think the best thing for all Democratic candidates, and what we're going to do in our campaign is, you heard me tonight, you didn't hear me say a word about any of the other candidates."

That might have been true in front of campaign audiences, but, even before the dust-up with Warren, Sanders spent weeks criticizing former Vice President Joe Biden as the two compete fiercely in Iowa and beyond. On Saturday, Biden called for Sanders' camp to "disown" what he calls "doctored video" that some of the senator's supporters say shows the former vice president endorsing Republican calls to cut Social Security and Medicare.

A short time later, Sanders' campaign manager, Faiz Shakir, responded that Biden needed to be honest about his record on Social Security.

Also Saturday, Warren campaigned in Iowa and addressed abortion rights, speaking to Planned Parenthood activists at a private home. She  told the crowd that she intentionally wore a pink Planned Parenthood scarf to Trump's inauguration, fashioned in such a way that the logo would show up any time she was photographed, according to a pool report of the gathering.

One of the people asking a question at the Planned Parenthood event, Tanya Keith of Des Moines, told Warren of the spat with Sanders:"I believe you 100%."

"Because I looked at you and I looked at him and I'm like, he did that. I know that Bernie Sanders said those things to you, because I have seen your body language and I've seen his body language," Keith said.

Warren responded, "Bernie and I've been friends for a long time."

"We fight for the same issues," she added. "We've been allies in these fights long before I ever got into politics."

House Democrats were preparing to outline their case for removing President Donald Trump from office in a legal brief due Saturday, as opposing sides in the impeachment case look ahead to the opening of the historic trial in the Senate.

Trump on Friday appointed several nationally known lawyers to the team that will defend him in the proceedings, set to open Tuesday afternoon.

The submission of the legal brief, due by 5 p.m. Saturday, follows the latest revelations in the case against Trump.

Democrats on Friday released more information — documents, text messages, audio and photos — turned over by Lev Parnas, an indicted associate of Trump lawyer Rudy Giuliani. The release included multiple photos of Parnas, a Soviet-born Florida businessman, posing with Giuliani or Trump or Donald Trump Jr., the president's son.

It included messages between Parnas and a staff member for Rep. Devin Nunes, R-Calif., a Trump ally who opposes the president's impeachment by the House. Parnas appeared to be connecting the staff member to Ukrainian officials who pushed unfounded corruption allegations against former Vice President Joe Biden.

The documents also raised more questions about the surveillance and security of former Ambassador Marie Yovanovitch. In them, an unidentified individual with a Belgian country code appears to describe Yovanovitch's movements.

The document release followed Thursday's announcement by the Government Accountability Office that the White House violated federal law by withholding congressionally approved security aid to Ukraine, which shares a border with a hostile Russia.

In response, the White House disagreed and said it does not have to follow decisions by the accountability office because it is an arm of Congress. White House officials also have noted that Trump eventually sent the $400 million in aid to Ukraine.

But the GAO report and Parnas documents intensified the pressure senators have been under to call more witnesses for the trial, a major source of disagreement between Democrats and Republicans that has yet to be resolved. The White House has instructed officials to disregard subpoenas from Congress seeking for them to appear as witnesses or turn over documents or other information.

Trump on Friday named Ken Starr, the prosecutor whose investigation two decades ago led to the impeachment of President Bill Clinton, along with former Harvard Law professor Alan Dershowitz, to his defense team.

The additions bring experience in the politics of impeachment as well as constitutional law to Trump's made-for-TV legal team. Both Starr and Dershowitz have been fixtures on Fox News Channel, Trump's preferred television network.

Dershowitz said he will deliver constitutional arguments defending Trump from allegations that he abused his power. Trump is also accused of obstructing Congress as it sought to investigate pressure he applied on Ukraine's president to announce an investigation into Trump's political rivals as the president withheld the security aid and a White House meeting as leverage.

Trump says he did nothing wrong and argues that Democrats have been out to get him since before he took office.

A legal brief from the White House laying out the contours of Trump's defense was due by noon Monday, and White House attorneys and Trump's outside legal team have been debating just how political the document should be.

Some in the administration have echoed warnings from Senate Majority Leader Mitch McConnell, R-Ky., that the pleadings must be sensitive to the Senate's more staid traditions and leave some of the sharper rhetoric exhibited during the House proceedings to Twitter and cable news.

Dershowitz is a constitutional expert whose expansive views of presidential powers echo those of Trump. Starr is a veteran of Washington's partisan battles after leading the investigation into Clinton's affair with a White House intern. The House impeached Clinton, who then was acquitted at his Senate trial. Trump is expecting the same outcome from the Republican-led chamber.

Still, the lead roles for Trump's defense will be played by White House counsel Pat Cipollone and Trump personal lawyer Jay Sekulow, who also represented Trump during special counsel Robert Mueller's Russia investigation.

Dershowitz sought to play down his role in the case in the hours after he was named to the team, saying he would be present for just about an hour to make the constitutional arguments.

"I'm not a full-fledged member of the defense team," he told "The Dan Abrams Show" on SiriusXM.

White House lawyers succeeded in keeping Trump from adding House Republican lawmakers to the defense team, but they also advised him against tapping Dershowitz, according to two people who spoke on condition of anonymity to discuss internal discussions. They're concerned about the professor's association with Jeffrey Epstein, the financier who killed himself in a New York City jail cell last summer while awaiting trial on sex trafficking charges.

A Fox News host said on the air that Starr would be parting ways with the network as a result of his role on the legal team.

Other members of Trump's legal defense include Pam Bondi, the former Florida attorney general; Jane Raskin, who was part of the president's legal team during Mueller's investigation; Robert Ray, who was part of the Whitewater investigation of the Clintons; and Eric D. Herschmann of the Kasowitz Benson Torres legal firm, which has represented Trump in numerous cases over the last 15 years.

Giuliani, a former New York-based federal prosecutor, told The Associated Press the president had assembled a "top-notch" defense team and he was not disappointed at being excluded from it.

Giuliani, who many in the White House blame for leading Trump down the path to impeachment by fueling Ukraine conspiracies, had previously expressed interest in being on the legal team. But he said Friday his focus would be on being a potential witness.

Trump was impeached by the House in December. Senators were sworn in as jurors Thursday by Chief Justice John Roberts, who will preside over the trial.

Starr, besides his 1990s role as independent counsel, is a former U.S. solicitor general and federal circuit court judge.

More recently, he was removed as president of Baylor University and then resigned as chancellor of the school in the wake of a review critical of the university's handling of sexual assault allegations against football players. Starr said his resignation was the result of the university's board of regents seeking to place the school under new leadership following the scandal, not because he was accused of hiding or failing to act on information.

Dershowitz's reputation has been damaged in recent years by his association with Epstein. One of Epstein's alleged victims, Virginia Roberts Giuffre, has accused Dershowitz of participating in her abuse. Dershowitz has denied it and has been battling in court for years with Giuffre and her lawyers. He recently wrote a book, "Guilt by Accusation," rejecting her allegations.

Giuffre and Dershowitz are also suing each other for defamation.

More than a thousand Central American migrants on Saturday surged onto a bridge spanning the Suchiate River between southern Mexico and Guatemala as Mexican National Guardsmen attempted to impede their journey north.

Mexican officials allowed several dozen migrants to enter the country via the bridge, while a voice over a loudspeaker warned that migrants may not be granted asylum in the U.S., even if they make it there.

Nearby, hundreds of guardsmen lined the river to prevent migrants from crossing into Mexico clandestinely. The voice on the loudspeaker warned, over and over, that those crossing the river "are entering Mexico illegally."

Mexico's government has said migrants entering the country without registering will not be allowed to pass from its southern border area. But those seeking asylum or other protections will be allowed to apply and legalize their status in Mexico.

Guatemalan officials have counted more than 3,000 migrants who registered at border crossings to enter that country in recent days and there were additional migrants who did not register.

The bridge to Mexico was closed on Saturday after being open on the previous day. Migrants who had wanted to cross and request asylum or seek to regularize their status and find work could do so.

But the migrants were wary of a trap. Mexico's offer of legal status and potential employment carries a stipulation that would confine them to southern Mexico, where wages are lower and there are fewer jobs than elsewhere in the country.

Meanwhile, Guatemala's human rights defender's office said there were more than 1,000 migrants gathering at another point on the Mexican border far to the north in the Peten region and there were reports that Mexican forces were gathering on the other side of the border there.

In the Mexican border town of Ciudad Hidalgo, Francisco Garduño, commissioner of Mexico's National Immigration Institute, was emphatic that migrants who try to enter the country irregularly would go no farther.

"They cannot enter because it would be in violation of the law," he told The Associated Press. He declined to talk specifics about border reinforcements, but said there were "sufficient" troops to keep things orderly.

The Federal Aviation Administration halted all flights in and out of Chicago's O'Hare Airport for hours Friday night due to a sprawling winter storm, which forced the closure of schools, universities and government offices as it moved across large sections of the Midwest.

The FAA lifted the stop at 9:45 p.m., but by then hundreds of flights already were canceled Friday at at one of the nation's busiest airports.

Earlier Friday, a plane slid off an icy taxiway at Kansas City International Airport. The Delta Air Lines flight was taxiing to be de-iced before flying to Detroit when the nosegear slipped off the taxiway, said Delta spokeswoman Martha Witt. There were no reports of injuries aboard the Airbus A319, which was carrying 123 passengers and a crew of six. Witt said the airline was trying to put passengers from Delta flight 1114 on other planes.

The airport was closed and numerous flights were canceled in the morning but flights resumed about noon. Most Friday flights from Nashville, Tennessee, were canceled, likely disrupting travel plans for fans of the Tennessee Titans flying into Kansas City for Sunday's AFC championship game with the Chiefs, KCTV reported.

At 9 p.m., the Chicago Department of Aviation was reporting nearly 690 flights had been canceled at O'Hare, with 169 flights cancelled at Midway, the city's other international airport. A winter weather advisory was issued for the Chicago area through early Saturday, with 2 to 5 inches of snow expected.

"If there is travel you don't need to make, consider postponing it,'' said meteorologist Ricky Castro.

Lambert lnternational Airport in St. Louis reported more than 130 flights canceled as of noon Friday and American Airlines suspended all flights to Missouri's Columbia Regional Airport until noon Saturday.

The slippery conditions come after the National Weather Service issued winter weather advisories, saying the storm will create hazardous travel conditions from the Plains into the Northeast through the weekend. Snow is forecast over much of the Great Lakes, with a blizzard warning for parts of the Upper Midwest.

The winter weather advisory extended south into western Oklahoma and northern Arkansas, where freezing rain was expected Friday.

In South Dakota and Minnesota, dozens of schools canceled classes Friday ahead of snowfall expected during the day.

In Kansas Gov. Laura Kelly closed state offices in the Topeka area, urging people in a news release to "stay safe and warm, exercise caution and allow road crews to do their job."

A storm that hit during the morning commute Friday coated the roads of Salt Lake City with up to 5 inches (13 centimeters) of snow. Advance warning allowed a delayed start for state government and some schools, which kept the number of crashes to a relatively low 75, police said.