Mr. Hurd, Mr. Kinzinger and Mr. Upton will be the lawmakers to watch. None agreed to be interviewed for this article. But all three have made noises that suggest they are open to impeachment. Mr. Hurd has said there is “damning” evidence against Mr. Trump, and on Sunday told Fox News that if he concluded that the president used his office to get damaging information on a political rival, he would “have to truly consider whether impeachment is the right tool or not.” Mr. Kinzinger said he wanted “to know what happened.” Mr. Upton has called the president’s actions on Ukraine “disconcerting.”

That they have fallen in line behind the president — at least for now — reflects the power of Mr. Trump’s base, and their fear of invoking the wrath of a vindictive president who could end their careers with a single tweet. While Trump voters may tolerate criticism of the president’s behavior or policies, impeachment is different.

“You tick off your base and you don’t win other-party support, so you get the worst of both worlds,” said Neil Newhouse, who has surveyed attitudes on impeachment for the House Republicans’ campaign arm…

“I look at this kind of like the Kavanaugh hearings,” Mr. Newhouse said, referring to the partisan battle last year over confirming Justice Brett M. Kavanaugh, who faced allegations of sexual assault but ultimately prevailed on a mostly party-line vote. “Both sides are going to put out their best stuff and everybody’s going to end up where they began.”