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George H.W. Bush’s surprise announcement at the GOP convention in 1988 that he had selected Sen. Dan Quayle of Indiana quickly overshadowed Bush himself when questions surfaced about Quayle’s service in the National Guard during Vietnam.

“Within hours, it was attracting all the ink and TV time we had counted on for George’s official rollout as nominee,” James Baker, Bush’s campaign chairman, wrote in his memoir.

Light said leaking names of serious contenders gives campaigns an opportunity to see what unsavory issues might be dredged up by interest groups and the press, and to find out whether the questions will peter out or mushroom. He likens it to entering a horse in lower-profile races before the Kentucky Derby.

“You want to see how your horse does under real conditions against strong competitors,” Light said.

Romney promises to reveal his decision on a running mate before the GOP convention in late August but won’t share much more.

When his wife was asked by CBS last week if she had a favorite candidate, she said: “I like to think that I have a few that I really like a lot.”

Romney himself would add just three words: “What she said.”

Associated Press writer Kasie Hunt contributed to this report.