His comments on Friday, the first he had offered since images emerged of one of Mr. Porter’s former wives bearing a black eye, were the culmination of a week’s worth of politically ill-advised steps that suggest that the president and his lieutenants cannot stop themselves from blunting positive political momentum. By the weekend, Mr. Trump’s State of the Union address, strong employment and wage figures as well as the onset of tax cuts seemed washed away by the latest White House controversy.

The frustration in the Republican political class is bursting forward.

“For members or anybody else who cares about keeping control of Congress, if you find yourself talking about anything but the middle-class tax cut, shut up and stop talking,” fumed Corry Bliss, who runs the primary House Republican “super PAC,” the Congressional Leadership Fund. “Any time spent on TV talking about anything but how we’re helping the middle class is a waste of time and does nothing to help us win in 2018.”