By a nearly 20-point margin, Republican and GOP-leaning likely voters chose Donald Trump over House Speaker Paul D. Ryan as to who better matches what they think the party should stand for, according to polling released Thursday.

Fifty-one percent of Republicans and GOP leaners said Mr. Trump’s view better matches their own view of what the Republican party should stand for, compared to 33 percent who chose Mr. Ryan, according to the Bloomberg Politics poll. Fifteen percent said they weren’t sure.

Mr. Trump’s favorable rating stood at 76 percent in the poll, which was down from 81 percent in late September. Mr. Ryan’s favorable rating was 50 percent - down 11 points since September.

Mr. Ryan has endorsed Mr. Trump, but has kept him at arm’s length, as has Senate Majority Leader Mitch McConnell.

Mr. Trump has campaigned on a platform of strict immigration policies and opposition to international trade pacts, while Mr. Ryan has been trying to unify the party around a “better way” House GOP agenda in areas like health care, tax reform, and national security.

“What is clear in these data is that a large segment of Trump supporters are all-in with the candidate. They see him as capable of delivering on the promise of a greater nation,” said pollster J. Ann Selzer, who oversaw the survey.

“That said, just 38 percent of them say they will stay loyal and follow his future endeavors if he does not win,” she said. “If he were to lose, our data suggest his standing would diminish.”

Indeed, Republicans were split on who should be the face of the Republican party nationally if Hillary Clinton defeats Mr. Trump in the presidential election.

Twenty-seven percent chose GOP vice presidential nominee Mike Pence, compared to 24 percent for Mr. Trump, 19 percent for Sen. Ted Cruz, 15 percent for Mr. Ryan, and 10 percent for Ohio Gov. John Kasich