WASHINGTON — The House impeachment managers formally triggered the start of former President Donald Trump's second impeachment trial Monday evening after they walked across the Capitol and delivered to the Senate the charge against Trump, the first president in history to be impeached twice.

Wearing black masks and walking two-by-two through the very halls where rioters had overtaken the Capitol earlier this month in a deadly siege, the impeachment managers were led into the Senate chamber by the lead impeachment manager, Rep. Jamie Raskin of Maryland, who read the article of impeachment.

The contours of Trump's Senate trial are starting to take shape as the ceremonial elements got under way, with the Senate's longest-serving Democrat expected to preside over the trial and Democrats still weighing whether to pursue witnesses during proceedings that could take up a chunk of February.

Chief Justice John Roberts will not be presiding like he did for Trump's first impeachment trial, according to two sources familiar with the matter. Instead, Sen. Patrick Leahy, the president pro tempore of the Senate, is expected to preside, the sources said. The Constitution says the chief justice presides when the person facing trial is the current president of the United States, but senators preside in other cases, one source said.

Following the triggering of Trump’s impeachment trial in Senate, Republican senators were easing off their criticism of the former president and shunning calls to convict him over the deadly siege at the US Capitol. It's an early sign of Trump's enduring sway over the party.

Republican denunciations of Trump have cooled since the Jan. 6 riot. Instead Republicans are presenting a tangle of legal arguments against the legitimacy of the trial and questioning whether Trump's repeated demands to overturn Joe Biden's election really amounted to incitement.

What seemed for some Democrats like an open-and-shut case that played out for the world on live television, as Trump encouraged a rally mob to “fight like hell" for his presidency, is running into a Republican Party that feels very differently.

Not only are there legal concerns, but senators are wary of crossing the former president and his legions of followers — who are their voters. Security remains tight at the Capitol. Sen. John Cornyn, R-Texas, asked if Congress starts holding impeachment trials of former officials, what's next: “Could we go back and try President Obama?”

Arguments in the Senate trial will begin the week of Feb. 8, and the case against Trump, the first former president to face an impeachment trial, will test a political party still sorting itself out for the post-Trump era.

Republican senators are balancing the demands of deep-pocketed donors who are distancing themselves from Trump and voters who demand loyalty to him. One Republican, Sen. Rob Portman of Ohio, announced Monday he would not seek reelection in 2022, citing the polarized political atmosphere.

For Democrats the tone, tenor and length of the upcoming trial, so early in Biden's presidency, poses its own challenge, forcing them to strike a balance between their vow to hold Trump accountable and their eagerness to deliver on the new administration's priorities following their sweep of control of the House, Senate and White House.

Biden himself told CNN late Monday that the impeachment trial “has to happen.” While acknowledging the effect it could have on his agenda, he said there would be “a worse effect if it didn’t happen.”

Earlier, Senate Majority Leader Chuck Schumer said failing to conduct the trial would amount to a “get-out-jail-free card” for others accused of wrongdoing on their way out the door.

Republicans appear more eager to argue over trial process than the substance of the case, he said, perhaps to avoid casting judgment on Trump's “role in fomenting the despicable attack” on the Capitol.

Schumer said there's only one question "senators of both parties will have to answer before God and their own conscience: Is former President Trump guilty of inciting an insurrection against the United States?”

Leaders in both parties agreed to a short delay in the proceedings that serves their political and practical interests, even as National Guard troops remain at the Capitol amid security threats on lawmakers ahead of the trial.

The start date gives Trump’s new legal team time to prepare its case, while also providing more than a month's distance from the passions of the bloody riot. For the Democratic-led Senate, the intervening weeks provide prime time to confirm some of Biden’s key Cabinet nominees.

Trump is still working on filling out his legal team, and one lawyer who had been approached declined to join on Monday. Sen. Lindsey Graham, a South Carolina Republican, said he spoke to Trump on Sunday while the former President was golfing in Florida.

Asked about Trump's mindset and preparations ahead of his second impeachment trial, Graham said, "Well, I think he'd like to get it over with." Graham said he "wouldn't think" Trump would come back from Florida for the proceedings, again emphasizing the desire for a quick trial.

Trump has begun to craft a defense strategy with Butch Bowers, the South Carolina lawyer who has agreed to represent him in the historic proceedings. Bowers, a respected lawyer from Columbia, South Carolina, who once worked in the Justice Department under President George W. Bush, has been in conversation with Trump in recent days.

Sen. Chris Coons, D-Del., questioned how his colleagues who were in the Capitol that day could see the insurrection as anything other than a “stunning violation” of the nation's history of peaceful transfers of power.

"It is a critical moment in American history,” Coons said Sunday in an interview.

Rand Paul of Kentucky said that without the chief justice presiding the proceedings are a “sham.” Joni Ernst of Iowa said that while Trump “exhibited poor leadership,” it's those who assaulted the Capitol who “bear the responsibility.” New Sen. Tommy Tuberville of Alabama said Trump is one of the reasons he is in the Senate, so "I’m proud to do everything I can for him.”

Sen. Tom Cotton, R-Ark., is among those who say the Senate does not have the constitutional authority to convict a former president.

Democrats reject that argument, pointing to an 1876 impeachment of a secretary of war who had already resigned and to opinions by many legal scholars. Democrats also say that a reckoning of the first invasion of the Capitol since the War of 1812, perpetrated by rioters egged on by a president as Electoral College votes were being tallied, is necessary.

A few GOP senators have agreed with Democrats, though not close to the number that will be needed to convict Trump.

Mitt Romney of Utah said he believes "what is being alleged and what we saw, which is incitement to insurrection, is an impeachable offense. ... If not, what is?” Romney was the only Republican senator to vote for conviction when the Senate acquitted Trump in his first impeachment trial. — Agencies