The attention-seeking West Virginia senator, who has teased a late third-party presidential bid, tried to keep up the suspense at a Friday appearance in the state.
More than three dozen incumbents have announced they will not seek re-election next year. Some are running for other offices, while others intend to leave Congress altogether.
While the party will be on defense in every competitive race, Republicans face some messy primaries and a recent history of nominating extreme candidates who have lost key contests.