Senator Thom Tillis of North Carolina, one of the Republicans most vulnerable incumbents, tried to turn around his faltering re-election campaign on Monday night, clashing with Cal Cunningham, his Democratic challenger, in a televised debate that largely focused on the coronavirus pandemic.
The contest in a key swing state is one of a handful of races that could determine control of the Senate next year, and almost every recent public poll shows Mr. Tillis, a first-term incumbent who is mostly allied with President Trump, trailing Mr. Cunningham, a former state senator and Iraq war veteran.
Seeking to halt that momentum, Mr. Tillis repeatedly tried to chip away at Mr. Cunninghams image as an inoffensive moderate, painting him instead as a craven, ladder-climbing liberal who would say anything to get elected.
Mr. Tillis implied Mr. Cunningham would defund the police, a position his rival rejected. He leaned heavily on his own status as an incumbent, highlighting bipartisan work done by Congress to provide relief to millions of Americans suffering from economic hardships caused by the coronavirus.
But Mr. Tilliss biggest break came without much effort when Mr. Cunningham said he would be hesitant to take a vaccine approved by federal health authorities because of extraordinary corruption in Washington that he said was warping science in favor of commercial interests.
Yes, I would be hesitant, but I am going to ask a lot of questions, he said, adding that he thought other Americans felt the same way given the way we have seen politics intervening in Washington.
Mr. Cunningham later clarified his remark, saying he would take a vaccine if the F.D.A. approved it and politics was not involved, but Mr. Tillis pounced, chastising Mr. Cunningham as irresponsible. Republican groups quickly began circulating a clip of the exchange on social media.
That statement puts lives at risk and it makes it more difficult to manage the crisis he pretends to say he is up to the task to manage, Mr. Tillis said. He said he would trust a vaccine and the scientists behind it.
Still, at other points Mr. Tillis found himself on the defensive over his record as the two men sought to reintroduce themselves to North Carolina voters.