WASHINGTON — Even as they are set to acquit President Trump in his impeachment trial this week, Senate Republicans appear to be increasingly breaking with his defense that he did nothing wrong.

On Sunday, Senator Lamar Alexander of Tennessee, who was a key vote against calling witnesses in the Senate trial, expanded upon his criticism that Mr. Trump was “crossing the line” in his pressure campaign against Ukraine. And Senator Joni Ernst of Iowa, who has remained a reliable defender of the president during his trial, called his actions “not what I would have done.”

A day before the first contest of the 2020 election, two days before Mr. Trump’s State of the Union address and three days before his expected acquittal, they and other Republicans appeared to be coalescing around a more nuanced argument: Mr. Trump’s efforts to push Ukraine into investigating a political rival while withholding critical military aid might not have been appropriate. But that did not warrant the president’s removal from office for the first time in American history.

“I think he shouldn’t have done it — I think it was wrong,” Mr. Alexander said Sunday on “Meet the Press” on NBC. “Inappropriate, was the way I’d say it. Improper, crossing the line. And then the only question left is: Who decides what to do about that?”