WASHINGTON — President Trump has never shown any reluctance to sacrifice a surrogate to serve a short-term political need, so he apparently did not think twice this week about exposing a series of staff members to ridicule as he repeatedly shifted his explanation for firing James B. Comey, the F.B.I. director.

Mr. Trump, obsessed with the F.B.I.’s investigation into Russia’s meddling in the 2016 election and increasingly frustrated by the hyper-scrutiny of the Washington press corps, is more in need of effective spokesmen than ever, and aides say he is considering a broad shake-up of his team.

But his career-long habit of viewing his public protectors as somewhat disposable, on vivid display after Mr. Comey’s sudden ouster, has not exactly been an incentive to step into the firing line on his behalf.

After the “Access Hollywood” scandal, Mr. Trump raged at Rudolph W. Giuliani, the former mayor of New York, for going on TV to defend him, arguing that he wanted to attack Hillary Clinton, not play defense. Corey Lewandowski, Mr. Trump’s 2016 campaign manager until he fired him, repeatedly groused to friends that he was forced to absorb all of the criticism for the campaign’s practice of confining reporters at rallies in small pens. Mr. Trump, he told two people close to him, had ordered him to do it — but placed the blame on Mr. Lewandowski when reporters complained about it.