Earlier in the day, Mr. Trump had asked on Twitter, “How do you impeach a president who has won perhaps the greatest election of all time?” He continued the theme at his news conference by asserting that “you can’t impeach somebody who is doing a great job.”

Ms. Pelosi and senior Democrats said they were determined not to take the bait for now and risk generating a backlash from Mr. Trump’s supporters, who would most likely see impeachment as the overreaction of out-of-control Democrats. But the words of Ms. Tlaib, who stood by her comments on Friday, made evident the pressure already mounting from the left, where public opinion polls suggest a majority of liberals want the president removed from office.

“People love you and you win,” Ms. Tlaib told the crowd Thursday night. “And when your son looks at you and says: ‘Momma, look, you won. Bullies don’t win.’ And I said, ‘Baby, they don’t.’ Because we’re going to go in there, and we’re going to impeach the motherfucker.”

She made no apologies for the remark on Friday, proclaiming that “I will always speak truth to power” and fashioning her own hashtag, #unapologeticallyme. She told a Detroit television station that “it’s probably exactly how my grandmother, if she was alive, would say it.”

Her outburst ran counter to all Democratic talking points. Ms. Pelosi and her deputies have repeatedly made the case that it is too early to consider impeachment. Even as Mr. Trump’s legal perils have deepened — and federal prosecutors in New York appear to have gathered evidence implicating him in a campaign finance crime — Democrats have said they want to wait to see the findings of an investigation by the special counsel, Robert S. Mueller III, of the president, his campaign and Russia’s attempts to interfere in the 2016 election.

“I don’t really like that kind of language,” Representative Jerrold Nadler, Democrat of New York and the chairman of the House Judiciary Committee — where any impeachment inquiry must begin — said on CNN. “But more to the point, I disagree with what she said. It is too early to talk about that intelligently. We have to follow the facts.”

Ms. Pelosi defended Ms. Tlaib on Friday at a town hall hosted by MSNBC at the speaker’s alma mater in Washington, Trinity University. “I’m not in the censorship business,” Ms. Pelosi said.