WASHINGTON >> House Speaker Nancy Pelosi said Sunday the House will proceed with legislation to impeach President Donald Trump, calling him a threat to democracy after the deadly assault on the Capitol.

Pelosi made the announcement in a letter to colleagues. She said the House will act with solemnity but also urgency with just days remaining before Trump is to leave office on Jan. 20.

“In protecting our Constitution and our Democracy, we will act with urgency, because this President represents an imminent threat to both,” she said.

“The horror of the ongoing assault on our democracy perpetrated by this President is intensified and so is the immediate need for action.”

With impeachment planning intensifying, two Republican senators want Trump to resign immediately as efforts mount to prevent Trump from ever again holding elective office in the wake of deadly riots at the Capitol.

House Democrats are expected to introduce articles of impeachment on Monday and vote as soon as Tuesday. The strategy would be to condemn the president’s actions swiftly but delay an impeachment trial in the Senate for 100 days. That would allow President-elect Joe Biden to focus on other priorities as soon as he is inaugurated Jan. 20.

Rep. Jim Clyburn, the third-ranking House Democrat and a top Biden ally, laid out the ideas Sunday as the country came to grips with the siege at the Capitol by Trump loyalists trying to overturn the election results.

“Let’s give President-elect Biden the 100 days he needs to get his agenda off and running,” Clyburn said.

Pressure was mounting for Trump to leave office even before his term ended amid alarming concerns of more unrest ahead of the inauguration. The president whipped up the mob that stormed the Capitol, sent lawmakers into hiding and left five dead.

Republican Sen. Pat Toomey of Pennsylvania joined Republican Sen. Lisa Murkowski of Alaska in calling for Trump to “resign and go away as soon as possible.”

“I think the president has disqualified himself from ever, certainly, serving in office again,” Toomey said. “I don’t think he is electable in any way.”

Murkowski, who has long voiced her exasperation with Trump’s conduct in office, told the Anchorage Daily News on Friday that Trump simply “needs to get out.” A third Republican, Sen. Roy Blunt, of Missouri, did not go that far, but on Sunday he warned Trump to be “very careful” in his final days in office.

Corporate America began to tie its reaction to the Capitol riots by tying them to campaign contributions.

Blue Cross Blue Shield Association’s CEO and President Kim Keck said it will not contribute to those lawmakers — all Republicans — who supported challenges to Biden’s Electoral College win. The group “will suspend contributions to those lawmakers who voted to undermine our democracy,” Kim said.

Citigroup did not single out lawmakers aligned with Trump’s effort to overturn the election, but said it would be pausing all federal political donations for the first three months of the year. Citi’s head of global government affairs, Candi Wolff, said in a Friday memo to employees, “We want you to be assured that we will not support candidates who do not respect the rule of law.”

House leaders, furious after the insurrection, appear determined to act against Trump despite the short timeline.

Late Saturday, Pelosi, D-Calif., convened a conference call with her leadership team and sent a letter to her colleagues reiterating that Trump must be held accountable. She told her caucus, now scattered across the country on a two-week recess, to “be prepared to return to Washington this week” but did not say outright that there would be a vote on impeachment.

“It is absolutely essential that those who perpetrated the assault on our democracy be held accountable,” Pelosi wrote. “There must be a recognition that this desecration was instigated by the President.”

Senate Majority Leader Sen. Mitch McConnell, R-Ky., has said an impeachment trial could not begin under the current calendar before Inauguration Day, Jan. 20.

Clyburn said that Pelosi “will make the determination as when is the best time” to send articles of impeachment to the Senate if and when they are passed by the House.

Another idea being considered was to have a separate vote that would prevent Trump from ever holding office again. That could potentially only need a simple majority vote of 51 senators, unlike impeachment, in which two-thirds of the 100-member Senate must support a conviction.

The Senate was set to be split evenly at 50-50, but under Democratic control once Vice President-elect Kamala Harris and the two Democrats who won Georgia’s Senate runoff elections last week are sworn in. Harris would be the Senate’s tie-breaking vote.

House Democrats were considering two possible packages of votes: one on setting up a commission to invoke the 25th Amendment to remove Trump from office and one on the impeachment charge of abuse of power.

Rep. Jim McGovern, D-Mass., who was part of the weekend leadership call, said he expected a “week of action” in the House.

While many have criticized Trump, Republicans have said that impeachment would be divisive in a time of unity.

Sen. Marco Rubio, R-Fla., said that instead of coming together, Democrats want to “talk about ridiculous things like ‘Let’s impeach a president’” with just days left in office.

Still, some Republicans might be supportive.

Nebraska Sen. Ben Sasse said he would take a look at any articles that the House sent over. Illinois Rep. Adam Kinzinger, a frequent Trump critic, said he would “vote the right way” if the matter were put in front of him.

The Democratic effort to stamp Trump’s presidential record — for the second time — with the indelible mark of impeachment had advanced rapidly since the riot.

Rep. David Cicilline, D-R.I, a leader of the House effort to draft impeachment articles accusing Trump of inciting insurrection, said Sunday that his group had 200-plus co-sponsors.

The articles, if passed by the House, could then be transmitted to the Senate for a trial, with senators acting as jurors to acquit or convict Trump. If convicted, Trump would be removed from office and succeeded by the vice president. It would be the first time a U.S. president had been impeached twice.

Potentially complicating Pelosi’s decision about impeachment was what it meant for Biden and the beginning of his presidency. While reiterating that he had long viewed Trump as unfit for office, Biden on Friday sidestepped a question about impeachment, saying what Congress did “is for them to decide.”

A violent and largely white mob of Trump supporters overpowered police, broke through security lines and windows and rampaged through the Capitol on Wednesday, forcing lawmakers to scatter as they were finalizing Biden’s victory over Trump in the Electoral College.

Toomey appeared on CNN’s “State of the Union” and NBC’s “Meet the Press.” Clyburn was on “Fox News Sunday” and CNN. Kinzinger was on ABC’s “This Week,” Blunt was on CBS’ “Face the Nation” and Rubio was on Fox News Channel’s “Sunday Morning Futures.”

PREVOUS COVERAGE:

WASHINGTON >> The latest on President Donald Trump and impeachment (all times local):

6:45 p.m.

House Speaker Nancy Pelosi says the House “will proceed” with bringing legislation to impeach President Donald Trump to the floor.

Pelosi made the announcement in letter late Sunday to colleagues.

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5:25 p.m.

President Donald Trump is ordering the U.S. flag to be flown at half-staff as a sign of respect for two U.S. Capitol Police officers who have died since last Wednesday’s violent protests at the Capitol, as well as all members of law enforcement across the nation.

In a proclamation Sunday, Trump says the show of respect will take place at the White House and all federal buildings through sunset on Wednesday.

The proclamation makes no mention of the rioting at the Capitol.

Trump cites Capitol Police Officers Brian D. Sicknick and Howard Liebengood.

Sicknick joined the U.S. Capitol Police in 2008, serving until his death Thursday after being attacked as rioters seething over Trump’s election loss stormed the Capitol, believing the president’s false claims of a rigged election.

Authorities announced the death of Liebengood on Sunday. It was not clear whether his death was connected to Wednesday’s events. Two people familiar with the matter said the officer’s death was an apparent suicide. They were not authorized to discuss the matter publicly and requested anonymity.

There were increasing calls for Trump to order flags to be flown at half-staff on federal facilities after House Speaker Nancy Pelosi ordered the same for the Capitol following Sicknick’s death.

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4 p.m.

Citigroup is pausing all federal political donations for the first three months of the year in light of Wednesday’s deadly siege on the U.S. Capitol by supporters of President Donald Trump.

In a memo to employees Friday, Citi’s head of global government affairs Candi Wolff said, “We want you to be assured that we will not support candidates who do not respect the rule of law.”

“We support engaging with our political leaders even when we disagree, and our PAC is an important tool for that engagement,” Wolff wrote, adding that the company previously donated $1,000 to the campaign of Republican Sen. Josh Hawley of Missouri in 2019, who represents a state in which Citi has a lot of employees.

Unlike other companies which have announced pausing donations to the 147 Republicans who opposed certifying President-elect Joe Biden’s election, Citi says it is pausing all federal contributions.

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3:25 p.m.

Former California Gov. Arnold Schwarzenegger is calling President Donald Trump a failed leader who “will go down in history as the worst president ever.”

In a video posted on social media Sunday, the Republican took solace that Trump’s presidency was coming to an end and “would soon be as irrelevant as an old tweet.”

He called for national unity and vowed his support for President-elect Joe Biden.

Schwarzenegger, best known for his movie roles as “Conan the Barbarian,” was elected governor in 2003 of the country’s largest state. During the video, Schwarzenegger likened American democracy to the sword he brandished in his movies.

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2:45 p.m.

The U.S. flag at the White House is now flying at half-staff after calls for the flag there and at other federal locations be lowered to honor U.S. Capitol Police Officer Brian Sicknick.

House Speaker Nancy Pelosi had already ordered flags at the Capitol lowered to half-staff in Sicknick’s honor and calls were growing for President Donald Trump to do the same at the White House.

Sicknick joined the U.S. Capitol Police in 2008, serving until his death Thursday after being attacked as rioters seething over Trump’s election loss stormed the U.S. Capitol, believing the president’s false claims of a rigged election.

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2:30 p.m.

The trade group representing one of the nation’s best known health insurance brands says it’s suspending political contributions to lawmakers who voted last week to reject the Electoral College results that cemented Democrat Joe Biden’s victory over President Donald Trump in the November election.

The Blue Cross Blue Shield Association represents 36 regional and local insurers who use the brand, together covering about 1 in 3 Americans.

In a statement, Kim Keck, the group’s CEO and president, says it will continue to support lawmakers and candidates in both political parties who “will work with us to build a stronger, healthier nation.”

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1:05 p.m.

Sen. Roy Blunt says he doesn’t see a need for congressional Republicans to hold President Donald Trump accountable for his role in promoting last week’s Capitol riot but warned him to “be very careful” in his last 10 days in office.

The Missouri Republican called Trump’s decisions and actions leading up to last Wednesday’s riot “clearly reckless.” But he says the U.S. should be “thinking more about the first day of the next presidency” of President-elect Joe Biden than on removing Trump from office.

Blunt says he doesn’t think Trump will act recklessly again. He told CBS’ “Face the Nation”: “My personal view is that the president touched the hot stove on Wednesday and is unlikely to touch it again.”

Biden will be sworn in on Jan. 20.

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11:55 a.m.

Democratic Rep. Hakeem Jeffries says President Donald Trump is out of control and should be immediately removed from office as a “clear and present danger to the health and safety of the American people.”

Jeffries, who chairs the House Democratic Caucus, says that as a coequal branch of government, it’s Congress’ job to keep Trump in check — whether by impeachment, demanding his resignation or pushing Trump’s Cabinet to invoke the 25th Amendment declaring him unfit to serve.

The New York Democrat says while Trump’s Twitter account may now be permanently suspended, the president still has access to the nation’s nuclear codes and other weapons of power.

Jeffries pointed to a “constitutional responsibility” to act. He told NBC’s “Meet the Press”: “Donald Trump is completely and totally out of control, and even his long-time enablers have now come to that conclusion.”

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10:10 a.m.

House Majority Whip Jim Clyburn says the House could vote this week to impeach President Donald Trump but delay sending the legislation to the Senate until after many of incoming President Joe Biden’s Cabinet secretaries are confirmed for their posts.

The South Carolina Democrat says “it may be Tuesday or Wednesday before action is taken, but I think it will be taken this week.”

Clyburn says he’s concerned that a Senate trial could distract from the process of confirming Biden’s nominees.

Mitch McConnell, the Senate’s Republican leader, has said an impeachment trial could begin as early as Jan. 20 — Inauguration Day.

Clyburn says House Speaker Nancy Pelosi will decide when to appoint impeachment managers and send the articles to the Senate. He says an option would be to give Biden the “100 days he needs to get his agenda off and running, and maybe we’ll send the articles sometime after that.”

Clyburn appeared on CNN’s “State of the Union” and “Fox News Sunday.”

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9:40 a.m.

A second Republican senator has called for President Donald Trump to step down in the wake of the Capitol rioting this past week.

This time it’s Sen. Pat Toomey of Pennsylvania. He’s calling on Trump to resign for what Toomey says would be the good of the country after the Capitol riot that was carried out by supporters of the president.

Toomey says resignation is the “best path forward, the best way to get this person in the rear view mirror for us.” But Toomey says he’s not optimistic that Trump will step down before his term ends on Jan. 20.

Toomey also says that Trump’s role in encouraging the riot is an “impeachable offense.”

Toomey is the second GOP senator to call for Trump to step down, joining Sen. Lisa Murkowski of Alaska.

Trump supporters who were angry over his loss to Democratic President-elect Joe Biden stormed the Capitol on Wednesday. Five people were killed.

Toomey was interviewed Sunday on CNN’s “State of the Union” and NBC’s “Meet the Press.”