“There is no political inconvenience exception to the United States Constitution,” Ms. Warren said, referring to the concern among many Democratic leaders that trying to impeach Mr. Trump would only fail in the Republican-led Senate and strengthen the president.

Mr. Sanders said, “There has got to be a thorough investigation” by House Democrats of Mr. Trump, and added that he wished that Republican senators had “the guts” to take action against the president.

Mr. Buttigieg said he believed the president had “made pretty clear he deserves impeachment,” but added, “I’m going to leave it to the House and Senate to figure that out.”

[Read more about how young people are organizing for 2020.]

The town hall-style forums at Saint Anselm College were a chance for college students to question Democratic candidates. (Ms. Warren and Ms. Klobuchar did not weigh in on voting rights because they spoke before Mr. Sanders.) Here are some of the highlights for each candidate.

Sanders backs voting rights for Boston bomber and rapists

Mr. Sanders said he believed that people in jail, even “terrible people” like the Boston Marathon bomber and sex assault offenders, should have the right to vote, a view that is likely to draw rebukes from both Republicans and some Democrats alike.

“I think the right to vote is inherent to our democracy. Yes, even for terrible people,” he said. “Because once you start chipping away, and you say, ‘Well that guy committed a terrible crime, not going to let him vote. Well that person did that, not going to let that person vote,’ you’re running down a slippery slope.”

“I believe that people commit crimes, they pay the price,” he added. “When they get out of jail, I believe they certainly should have a right to vote. But I do believe that even if they are in jail, they are paying their price to society, but that should not take away their inherent American right to participate in our democracy.”