McCain joked on his campaign bus in Annapolis that his list had “every name imaginable” on it and stood at about 20 people but that there were probably a hundred people who thought they were on it. As nervous aides looked on and occasionally interjected to say that no decisions had been made, McCain said he had spoken with several people about heading the search for a running mate.

He broached the subject in a radio interview on Wednesday with Don Imus. “We just started this process of getting together a list of names and having them looked at, and I don’t know how long it takes,” he said. “But if I had a personal preference, I’d like to do it before the convention to avoid some of the mistakes that I’ve seen made in the past, as you get into a time crunch and maybe sometimes don’t make the announcement right.”

Choosing a conservative running mate might help McCain energise the Republican base.

Officials who have been mentioned include Secretary of State Condoleezza Rice and several governors, like Tim Pawlenty of Minnesota, Charlie Crist of Florida, Jon Huntsman Jr. of Utah and Mark Sanford of South Carolina. Former governors have also been mentioned, including Tom Ridge of Pennsylvania, whose support of abortion rights could cause trouble among conservatives already wary of McCain, and former primary opponents, Mitt Romney of Massachusetts and Mike Huckabee of Arkansas.