The impeachment trial for former President Trump kicked off in the Senate on Tuesday, beginning with debate over the constitutionality of the House prosecuting a president who has already left office.

The bottom line: After four hours of arguments by each side, the Senate affirmed by a vote of 56-44 that it is constitutional to try a former president.

• Six Republicans voted with Democrats, including Sen. Bill Cassidy (R-La.), who had previously voted "no" on the question.
• “Trump’s team was disorganized ... they did not talk about the issue at hand,” he told reporters. “As an impartial juror, I’m going to vote for the side that did the good job.”
• The others were Sens. Mitt Romney (Utah), Susan Collins (Maine), Lisa Murkowski (Alaska), Pat Toomey (Penn.) and Ben Sasse (Neb.)

Highlights:

• The Senate updated its organizing resolution to have the chamber convene every day until a verdict is rendered, after Trump lawyer David Schoen withdrew a request to break for the Jewish Sabbath.
• Lead impeachment manager Raskin played a video montage of Trump speaking at the Jan. 6 "Stop the Steal" rally, followed by footage of the violent mobs ransacking the Capitol. Some of the rioters were heard chanting, ""We are listening to Trump, your boss!"
• Raskin cited some of "the nation's most prominent conservative legal scholars," including former 10th Circuit Judge Michael McConnell, Federalist Society co-founder Steven Calebresi, GOP lawyer Charles Cooper and hundreds of others who have said it is constitutional to impeach and try an official after they've left office.
• Raskin also listed examples of Constitutional framers discussing the standard of impeachment, and how it was "inconceivable" that it could cease to apply during a president's last days in office. "President Trump may not know a lot about the framers. But they knew a lot about him," Raskin declared, pointing to their focus on "presidential corruption aimed at elections."
• Raskin, who lost his son to suicide just days before Jan. 6, concluded the Democrats' arguments with an emotional appeal as he detailed his family's experience at the Capitol during the insurrection.

The other side: Trump's lead counsel Bruce Castor opened his arguments at 3 p.m. with praise for the impeachment managers' "outstanding presentation," adding that no member of the Trump team will voice anything but condemnation of the rioters on Jan. 6.

• In a meandering opening speech, Castor argued Democrats want to convict Trump because they fear he’ll run again in 2024. Toward the end of his speech, he conceded: “We changed what we were going to do on account that we thought that the House managers' presentation was well done."
• Castor's main argument is that the electoral system worked and Democrats got what they wanted — to remove Trump from office — as he lost the election to Joe Biden.
• Lawyer David Schoen showed a video of Democrats calling to impeach Trump starting in 2017 and argued that the House moved to do a "snap impeachment" following the Jan. 6 insurrection.
• Schoen charged that because Trump is now a private citizen and cannot be removed from office, the trial is unconstitutional. He added that the former president is being deprived of due process, including because the presiding officer — Sen. Patrick Leahy (D-Vt.) — is also a juror.

The big picture: Trump will almost certainly be acquitted, absent any late and groundbreaking evidence against him. Instead, both sides will be playing to a jury outside the Capitol — the court of public opinion.

• Both Democrats and Republicans want to wrap the trial up quickly. Republicans don't want to spend any more time focusing on Donald Trump, and Democrats are eager to reframe the narrative around Biden's agenda and move forward with confirming his nominees.
• As required by Senate rules, the trial will become the chamber's main focus over the next few days. All other activity will be forced to take a back seat.

On the opposite end of Pennsylvania Avenue, Biden continued to distance himself from the trial. He met with business leaders about his $1.9 trillion coronavirus relief proposal.

Go deeper:

• Read the Trump legal team's latest impeachment brief
• Read the House's latest impeachment brief

This story is developing. Please check back for updates.