Still, the success of the infrastructure effort was a notable — if tentative — move away from Mr. Trump. It suggested that at least some Republicans now believe there is more political upside to be gained from breaking with him than from siding with him unquestioningly, a shift from the calculus that drove them for years.

“I think they take their jobs more seriously than he ever took his,” said Republican strategist Scott Jennings, a former top campaign aide to Mr. McConnell, explaining why senators in his party were not swayed by Mr. Trump’s latest attacks.

Mr. Jennings said their motivation was not so much defying the former president as trying to undercut Democrats’ argument in favor of eliminating the filibuster — namely, that the G.O.P. is a party of unreasonable and irresponsible acolytes of Mr. Trump who will reflexively reject any proposal that Democrats support. (Mr. McConnell is particularly insistent on preserving the rule setting a 60-vote threshold to advance legislation.)