WILKES-BARRE, Pennsylvania (AP) — Larry Mitko voted for Donald Trump in 2016. But the Republican from Beaver County in western Pennsylvania says he has no plans to back his party’s nominee for Senate, Dr Mehmet Oz — “no way, no how.”

Mitko doesn’t feel like he knows the celebrity heart surgeon, who only narrowly won his May primary with Trump’s backing. Instead, Mitko plans to vote for Oz’s Democratic rival, Lieutenant Governor John Fetterman, a name he’s been familiar with since Fetterman’s days as mayor of nearby Braddock.

“Dr Oz hasn’t shown me one thing to get me to vote for him,” he said. “I won’t vote for someone I don’t know.”

Mitko’s thinking underscores the political challenges facing Trump and the rest of the Republican Party as the former president shifts to general election mode with a rally Saturday night in Wilkes-Barre, Pennsylvania, the first of the fall campaign.

Hours before Trump was to speak, the crowd streamed into the 10,000-seat Mohegan Sun Arena. Doug Mastriano, the GOP’s hard-line nominee for governor of Pennsylvania, was already there, as was Trump ally Rep. Marjorie Taylor Greene, R-Ga..

While Trump’s endorsed picks won many Republican primaries this summer, many of the candidates he backed were inexperienced and polarising figures now struggling in their November races. That’s putting Senate control — once assumed to be a lock for Republicans — on the line.