In recent weeks, they have put the weight of the presidency behind an effort to persuade Georgia’s governor to appoint Representative Doug Collins, currently the top Republican on the House Judiciary Committee, to the state’s soon-to-be vacant Senate seat.
Mr. Collins has actively jockeyed for the appointment, which would not only put a reliable defender of the president into a key Senate position before a trial, but could allow someone like Representative Jim Jordan of Ohio or Representative John Ratcliffe of Texas, pugnacious faces of Mr. Trump’s impeachment defense so far, to replace Mr. Collins on the House Judiciary Committee as the impeachment process shifts there.
The ascension of Mr. Jordan or Mr. Ratcliffe would also create another vacancy that Republican leaders could fill with a defender of the president like Representative Mark Meadows of North Carolina.
But even without the reinforcements, congressional Republicans — many of whom are wary of incurring the president’s wrath and being punished for it by their party — have either echoed the White House claims against witnesses or found other ways to try to maintain focus on the Bidens, often in starkly personal terms.
Senator Marsha Blackburn of Tennessee, who has bound herself to Mr. Trump, used Twitter to attack Lt. Col. Alexander S. Vindman, a National Security Council official who was on the July 25 call the president held with Mr. Zelensky, and testified this week that he was immediately alarmed by the request for an investigation into the Bidens.
“Vindictive Vindman is the ‘whistle-blower’s’ handler,” Ms. Blackburn tweeted, referring to the anonymous government official whose concerns about the call prompted the House impeachment inquiry.
Senator Lindsey Graham of South Carolina, the chairman of the Senate Judiciary Committee and a key ally of Mr. Trump’s, has shown his support for the president in other ways.
On Friday, Mr. Graham announced plans to call Hunter Biden as a witness in a Senate trial.
Nicholas Fandos contributed reporting.