Russia, Mr. Treece said, was plainly “guilty of something.” But he hastened to add this: He hopes whichever candidates win in November will stand by the president, as he plans to.

So it went in interviews with Republican voters across the country on Monday and Tuesday, most of them devoted to the president’s policies generally. They quickly sorted themselves into two camps: those who winced at the episode, or at least questioned it, and those who continued to defend Mr. Trump without hesitation.

If history is a guide — and polling, too — the second group is significantly larger within the party. And for Mr. Trump’s true loyalists, the Helsinki meeting and its aftermath have once more inspired a sense of fury and grievance on his behalf. It is not merely that they support the president in spite of his Russia stance, like Republican lawmakers who grimace at times but largely embrace his agenda. Increasingly, these voters have absorbed Mr. Trump’s every viewpoint, his scapegoats, even his language tics as their own.

“It is strictly a witch hunt,” said Carol Livingood, 74, of Danville, Ind., who says she owns enough “Make America Great Again” hats and shirts to “wear Mr. Trump” every day of the week. “It makes Watergate look like playing in the sandbox.” She blamed the news media and the F.B.I. for stoking tensions.

“They’re just trying to make Trump’s election look fraudulent,” said Vernon Hastings Jr., 76, from Shreveport, La., calling reports of Russia’s election interference overblown. “You think it ain’t happening already? You think China’s not fooling with it?”

Several people said that Mr. Trump was only hoping to ratchet down tensions with a nuclear power, as they believe he did with Kim Jong-un of North Korea. His defense of Russia, they suggested, was strategic, even winking — part of a long game that most could not yet understand.