But it’s not just the crowds who seem to be taking their cues from the president.
On Friday, Senator David Perdue of Georgia, a wealthy former business executive who has a home in affluent Sea Island, Ga., took the microphone at a Trump rally in Macon, Ga., and sought to rile up the red-hatted audience. He suggested he did not know how to pronounce the name of Senator Kamala Harris, the Democratic vice-presidential nominee, with whom he has served in the Senate for over three years.
“Kamala? Kamala? Kamala-mala-mala?” he said. “I don’t know. Whatever.”
Democrats pounced, Republicans were put on the defensive and Mr. Perdue’s opponent, Jon Ossoff, raised over $1.8 million as of Sunday evening.
Mr. Trump’s staff has sought to mitigate his self-destructive tendencies. It is clear when he is speaking from a teleprompter at rallies, and as discursive as his speeches are, he’ll deliver many of his attack lines on Mr. Biden as written.
But at nearly every event, the president overwhelms his critique of the former vice president.
With Republicans desperate to reframe the election as a choice on policy differences, Mr. Trump, with his rhetorical outbursts, is effectively ensuring that the campaign remains a referendum on his conduct. That’s what alarms G.O.P. candidates and strategists, who fear that even the Supreme Court nomination of Judge Amy Coney Barrett is no match for Mr. Trump’s daily exercise in self-sabotage.
Returning to South Carolina triumphantly on Friday after he shepherded Ms. Barrett through her Judiciary Committee hearings, Senator Lindsey Graham held a rally-cum-news-conference that amounted to a victory lap. Locked in an unexpectedly close race for re-election against a Democrat, Jaime Harrison, who is raising record-breaking sums of money, Mr. Graham said he thought Mr. Trump would help him in the conservative-leaning state.
But as he stepped into an S.U.V. to leave, he acknowledged the undeniable.
“He can be a handful,” Mr. Graham said of Mr. Trump. “He can get in the way of his own success.”
A number of senior Republican strategists believe the president’s behavior will all but assure his own defeat and is likely to hand Democrats control of the Senate. And every time he criticizes a Republican lawmaker — as he did last week with Senators Ben Sasse of Nebraska and Susan Collins of Maine — they worry it will compound their losses.