The day after President Biden melted down in Thursday’s prime-time debate, Gov. Glenn Youngkin of Virginia stood beside former President Donald J. Trump on a farm in Chesapeake, gushing.

“This is the best Trump rally ever!”

In the past, when it suited him, Mr. Youngkin kept his distance from Mr. Trump and his unpredictable behavior.

Not now. Not with all this winning afoot.

“Hello, Virginia,” Mr. Trump cooed as he took the stage before thousands of his supporters in what Republicans increasingly see as a winnable state. “Did anybody watch a thing called the debate?” He roared: “That was a big one.”

On the surface, the rally in Chesapeake was a quick-turn victory lap after the debate and before the 2024 race hits a higher gear.

“Democrats are in a lot of trouble, so I feel pretty good today,” said Jason Alter, 35, a dentist from Miami.

But beneath the jubilation, there was a low-grade panic stirring. It was the kind of panic that one sometimes feels when everything in life seems to be going … a little too well.