And in the Kentucky governor’s race on Tuesday, Democrats carried the home counties of Louisville and Lexington by nearly triple the margin they ran up in the 2015 governor’s race. Four years ago, too, the Republican candidate for governor, Matt Bevin, carried the conservative Kentucky suburbs south of Cincinnati; this time around, two of those three counties broke for the Democratic candidate, Andy Beshear.

Mr. Bevin, who was on the ballot this week seeking a second term as governor, is now about 5,100 votes behind Mr. Beshear, who has claimed victory. Mr. Bevin on Wednesday formally asked state officials to undertake a check and recanvass of the voting machines and absentee ballots in the race, citing “irregularities” without providing details.

For Mr. Trump and other Republican leaders, the ongoing political realignment of the suburbs — which was essential to Democrats flipping Republican-held congressional seats in 2018 and retaking the House — is a disconcerting disadvantage that they have shown little ability to reverse. Democratic officials, in turn, increasingly believe they can press a center-left agenda with little risk of backlash because moderate voters will remain in their grip as long as Mr. Trump is in office and effectively make the G.O.P. a no-go zone for this demographic.

“Our coalition is growing and is more secure,” said Gov. Gina Raimondo of Rhode Island, the chair of the Democratic Governors Association, before quickly adding that Democrats cannot take their new voters for granted. “You have to earn it,” said Ms. Raimondo, counseling her party’s candidates to avoid ideological purity tests and instead focus on conveying to voters “that we’re going to do a better job making their lives easier.”

But she couldn’t help noting one factor behind the party’s good fortune. “Even some Republicans are just done with President Trump,” she said.