Congress is treading on new ground. No president has been impeached twice. What's more, no president has been tried by the Senate after he has left office. That question of whether a president no longer in office can be tried for impeachment is a huge issue that divides constitutional scholars over what is legally permissible.
Democrats have said a trial is necessary to ensure accountability for the attack. If Trump is convicted, the Senate could hold a second vote to disqualify him from seeking office again.
But Republicans say the trial is moot, given that Trump is out of office. And they argue the trial is unconstitutional.
What the trial will look like is yet to be seen. House Democrats on Thursday asked Trump to testify under oath for the trial. Trump later that day declined.
Here's a look at how things could turn out.
What would it take to convict Trump?
At least two-thirds of the Senate, or 67 votes, is needed to convict Trump. This is a particularly high hurdle for the prosecution to overcome given that the Senate is essentially split 50-50 between Republicans and Democrats. A total of 17 Republican senators would have to break ranks with the majority of the party to vote to impeach Trump.
While members of the Senate have traditionally not been as populist as the House, there is still quite a bit of support for Trump in the Republican party and among Senate Republicans, who fear primary challenges if they were to cross Trump and vote for conviction.
An early sign of just how tough that hurdle could be came on Jan. 26 when two-thirds of Republican senators voted against a measure that would have halted the chamber from moving forward on impeachment.
Just as a reference, Republican Sen. Mitt Romney of Utah was the sole Republican to break with his party to vote to convict Trump for abuse of power in the first impeachment trial. But Romney along with four other Republican Senators voted to kill the objection to forgo this second impeachment trial. Those other senators were Susan Collins of Maine, Lisa Murkowski of Alaska, Ben Sasse of Nebraska and Pat Toomey of Pennsylvania.
There's still a big question about how Republican minority leader Mitch McConnell of Kentucky may vote.
Last month, McConnell publicly blamed Trump in part for feeding "lies" to the mob that stormed the Capitol. He privately signaled he may be open to conviction. But then he sided with the measure put forth by Sen. Rand Paul, a fellow Republican from Kentucky, that said the trial is unconstitutional.
"I'm going to listen to the arguments," McConnell has reportedly said. "That's what we ought to do. That's what I said before it started. That's still my view. The issue on which we already voted is an interesting constitutional question. I think we ought to listen to the lawyers argue the question."
What would a conviction mean?
Given that Trump is no longer president, a conviction wouldn't remove him from office. But it would be a very public rebuke of his actions following the election and leading up to the riot.
A conviction would not result in Trump losing any of his benefits as a past president. The Former Presidents Act, passed in 1958, spells out the benefits that past presidents are entitled to, and it only withholds certain privileges, such as his pension and Secret Service detail, if a president is removed or terminated from service by impeachment and conviction. Trump's term was not terminated that way, so a conviction means he would still be entitled to these perks.
What about other 'punishments' resulting from a conviction?
If the Senate were to convict, it could hold another vote to disqualify Trump from holding federal office in the future. This vote would only require a simple majority. This would prevent Trump from running again for president again in 2024, as he has indicated he might do. He also wouldn't be able to run for a House seat or Senate seat if he's barred from holding federal office.
Of course, the vote to bar a president from holding office hasn't ever been tested before. No US president has ever been convicted of impeachment. And the Senate has never voted to bar a former president from holding office again. So if this scenario were to play out, there could be a lawsuit challenging this vote in court.
Another thing to keep in mind is that if Trump were convicted and the Senate voted to bar him from federal office, his influence could still loom large in American politics. He could still offer commentary and endorsements, as well as hold rallies. In other words, a vote to stop him from running for office again wouldn't necessarily mean the end of Donald Trump and the MAGA movement.
What happens if Trump is acquitted?
As happened in his first impeachment, Trump could be acquitted by the Senate. This vote to acquit wouldn't mean much in practical terms, since he is no longer president. But it would likely serve as another rallying cry for Trump and his base just as the previous acquittal was.
An acquittal would also mean that the Senate would not vote to bar him from running for federal office. So Trump could, in theory, make a run for the presidency in 2024.
Could Trump be censured?
Yes. The Senate could vote to censure, which is simply a formal statement of disapproval. The consequence of censure is nonbinding, which means there are no legal ramifications. But it's a formal mode of disciplining a public official, such as a US president. And it serves as a kind of public shaming.
There are a handful of lawmakers who have pushed for censure. Sens. Tim Kaine, a Democrat from Virginia; Chris Coons, a Democrat from Delaware; and Maine's Susan Collins have floated this idea.
Senate Majority Leader Chuck Schumer of New York hasn't shut the door on censure if Democrats can't get a conviction.
"I think the president should be tried. I hope he will [get a] vote to be convicted," Schumer told reporters last week. "Anything past that is something we can discuss, but he deserves conviction, nothing less."
But it's still unclear if Democrats would go this route if they fail to get the votes to convict.