Several Republican lawmakers fell in line on Sunday behind President-elect Donald J. Trump’s plan to choose Kash Patel to lead the F.B.I., defending the incoming president’s right to install a loyalist who has vowed to use the position to exact revenge on Mr. Trump’s adversaries.

Mr. Trump’s announcement on Saturday that he intends to replace Christopher A. Wray, the current F.B.I. director, who still has three years left on his 10-year term, with Mr. Patel has stunned Democrats and many in the national security establishment. Mr. Patel has said he would launch a sweeping campaign of retribution against F.B.I. agents, journalists and others.

F.B.I. directors are confirmed by the Senate, and Mr. Patel is likely to face tough questions at his confirmation hearings about whether the agency would remain free from political interference. While Republican Senate leaders remained quiet on Sunday, other senators in Mr. Trump’s party expressed their support.

Senator Bill Hagerty, Republican of Tennessee, said he had encouraged Mr. Trump to appoint Mr. Patel.

“There are serious problems at the F.B.I.,” Mr. Hagerty said on NBC’s “Meet the Press.” “The American public knows it. They expect to see sweeping change, and Kash Patel is just the type of person to do it.”

Senator Ted Cruz, Republican of Texas, called Mr. Patel “a very strong nominee” to take on what he and other allies of Mr. Trump claim has been partisanship inside the F.B.I. because of its investigations into wrongdoing by the president-elect and his associates.

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