Separate but simultaneous vetting processes are underway. Advisers to Sen. Ted Cruz of Texas and Ohio Gov. John Kasich said they are developing a list of prospects and researching their backgrounds. They are leaving open the possibility of announcing running mates as early as June, when primary voting concludes, or waiting until July at the Republican National Convention.

Front-runner Donald Trump said he is giving the choice of a running mate serious thought, but his campaign is holding off on vetting candidates until the nomination battle is over. “I would not choose a vice president unless I know I have won,” Trump said in a recent interview.

A contested convention in Cleveland would mean that instead of focusing on a running mate that would most improve their chances of swaying voters nationwide in November, the candidates may first consider whether someone will help them win over delegates.

The candidates must also game out the timing. Do they name someone ahead of the convention, as Ronald Reagan did with an unsuccessful result in 1976?