“It’s no longer just the Mueller investigation,” Ms. Warren said. “They’re everywhere and these are serious investigations, so we’ll see what happens.”

In addition to the investigation by Robert S. Mueller III, the special counsel, into Russian interference in the 2016 election, there are continuing investigations spearheaded by federal prosecutors in New York and by the Democratic majority in the House of Representatives. Mr. Trump has denied any wrongdoing related to the 2016 campaign and Russia, and there is no indication that the president himself could be indicted or incarcerated before the 2020 election.

Ms. Warren’s remark was an unusually blunt jab at Mr. Trump, from a candidate who has largely declined to spar personally with the president since her entry into the 2020 race. Mr. Trump has repeatedly ridiculed Ms. Warren, often in personal terms and with racist slurs, for having in the past identified herself as having Native American ancestry. Ms. Warren recently apologized to the Cherokee Nation for having done so.

On Saturday, Mr. Trump appeared to invoke the Trail of Tears, the infamously cruel forced relocation of Native Americans in the early 19th century that caused thousands of deaths, when he mocked Ms. Warren on Twitter: “See you on the campaign TRAIL, Liz.” Ms. Warren did not refer explicitly to the Twitter post on Sunday.

[For those who need a refresher, here is a brief history of the Trail of Tears.]

Aside from the imprisonment crack, Ms. Warren spent little time in Iowa discussing Mr. Trump’s legal issues and caustic persona. She played down talk of impeachment and stressed to reporters that she was focused on “structural” problems that “were broken long before Donald Trump got here.”