Across the country, suburban voters’ disgust with Mr. Trump — the key to Mr. Biden’s election — did not translate into a wide rebuke of other Republicans, as Democrats had expected after the party made significant gains in suburban areas in the 2018 midterm elections. From the top of the party down to the state level, Democratic officials are awakening to the reality that voters may have delivered a one-time verdict on Mr. Trump that does not equal ongoing support for center-left policies.

“There’s a significant difference between a referendum on a clown show, which is what we had at the top of the ticket, and embracing the values of the Democratic ticket,” said Nichole Remmert, Ms. Skopov’s campaign manager. “People bought into Joe Biden to stop the insanity in the White House. They did not suddenly become Democrats.”…

“In 2018 in the Philadelphia suburbs, you had rage voting against Trump,” said Senator Bob Casey Jr. of Pennsylvania, a Democrat. But this year, with Mr. Trump on the ballot, the president brought out many more supporters who are occasional voters, diluting what Democrats had widely anticipated would be another wave election for them. “It may be suburban voters are still ticket splitters,” Mr. Casey said.