The U.S. Senate is expected to begin the second impeachment trial against former President Doanld Trump today for his alleged role in last month's insurrection on the Capitol building. GBH Morning Edition host Joe Mathieu spoke with Northeastern University law professor and GBH News legal analyst Daniel Medwed about this second trial and why the move to impeach the former president again is constitutional, despite some claims that it's not. The transcript below has been edited for clarity.

Joe Mathieu: The big question is whether it's constitutional to impeach someone who's no longer in office. And we want to get to this this morning because a lot of people have been talking around this. What are the main arguments, Daniel, that it is constitutional?

Daniel Medwed: The main arguments are grounded in the text of the Constitution and in public policy. And we're going to see them in their full glory today because the Senate may devote up to four hours yes, four hours to debating this precise issue. So first, just looking at the text, Articles One and Two of the Constitution talk about impeachment. Nowhere do they expressly limit this power to sitting or current office holders. And a long standing trope of legal argument is, if a law doesn't tell you you can't do something, you basically have the green light unless a court or some other entity tells you otherwise. Second, and I think more compelling, [is] public policy. A lot of people point out the perverse incentives that would be created if you couldn't impeach someone who has just left the office. Jamie Raskin, the House manager, says there's no January exception to impeachment. The idea is that people might be emboldened to engage in misbehavior in the dwindling days of their tenure knowing full well that they couldn't be held accountable through impeachment, at least. And finally, contrary to what Trump's team argued in some of their filings yesterday, this case isn't moot just because Trump is now a private citizen. Among the punishments for impeachment, of course, [are] not just removal from office, but also disqualification from holding future federal office. And since Trump is, of course, a one-term president, he otherwise would be eligible to run again in 2024. So this is a very consequential proceeding.

Mathieu: All right. But I wonder if there are any examples of trying to impeach a president or another federal official who was out of office at the time?

Medwed: There are a few comparisons. I think the most apt one comes from 1876. I believe we talked about this way back during the insurrection. At that time, William Belknap, the secretary of war, was being investigated for corruption by Congress. He tendered his resignation to President Grant just on the eve of the moment that Congress was about to impeach him. Even though he left office, Congress went ahead; the House voted to impeach and sent those articles of impeachment to the Senate. Much like today, the Senate then debated the constitutionality of going after a former officeholder, and by a narrow vote I believe it was 37 to 29 it decided that they could proceed, that there was jurisdiction. So they tried Belknap and, incidentally, he was acquitted.

Mathieu: Daniel, a lot of people have brought up the example of Belknap. Is there an argument that his case is distinguishable from the one against Trump, that a president is different than a cabinet secretary?

Medwed: That's a fascinating question because the two positions, of course, are incredibly different in terms of their portfolio, how you get the job and so on. But as a constitutional matter, there's no distinction between the president, the vice president and lower civil officers of the United States. They're all lumped in together as a single category. Plus, I think the case against Trump as a constitutional matter is even stronger because the House did vote to impeach him while he was still president about a week before he handed the reins grudgingly over to President Biden.

Mathieu: So how will the constitutional question be resolved? That's a simple majority, correct? We'll have that done, I'm assuming, pretty quickly.

Medwed: Absolutely. That should be done today. A simple majority vote, then the case can go for a full trial.