Democrats fretted Wednesday over whether their party had suffered a meaningful setback in its effort to hold control of the U.S. Senate with the decision by one of their marquee candidates, John Fetterman of Pennsylvania, to take the debate stage Tuesday night while still recovering from a stroke.

The state’s lieutenant governor stumbled often over his words and spoke haltingly, displaying communication challenges that contrasted sharply with the onstage skills of his opponent, Republican Mehmet Oz, the celebrity doctor who has spent hundreds of hours in front of TV cameras as host of “The Doctor Oz Show,” which ran for 13 seasons.