Among those urging Mr. Trump to spare Mr. Sessions have been Reince Priebus, the White House chief of staff; Stephen K. Bannon, the president’s chief strategist; and Donald F. McGahn II, the White House counsel, according to officials who asked not to be named describing internal deliberations.

For the White House, the attacks on the attorney general have touched off a serious problem on Capitol Hill when it did not need any other headaches. Senate Republicans who almost never link arms in unison against a president from their party formed a cordon around Mr. Sessions, making it clear that they neither concurred with nor would tolerate Mr. Trump’s repeated threats to the attorney general’s tenure. Senate leaders made clear they would block Mr. Trump from replacing Mr. Sessions if he tried to do so during the coming recess.