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But why let that spoil the fun, especially in the dog days of summer?

“It’s the quadrennial parlor game, where anyone who knows anything isn’t talking and people talking the most know nothing,” said Charlie Cook, head of the Cook Political Report.

His bet? Mr. Portman or Mr. Pawlenty.

“My gut tells me that Romney will be looking for a very solid, seasoned person with executive experience, will not be looking to make a showy splash or chase after a particular demographic,” Mr. Cook said. “Romney is not an ‘outside the box’ guy, not a long bomb thrower. While Romney doesn’t excite the conservative base, he doesn’t need to reach to his right because President Obama excites the conservative base.”

Asked about the circus over Mr. Romney’s vice-presidential pick, Larry Sabato, director of the University of Virginia’s Center for Politics, said, “Truth abhors a vacuum, but speculation thrives in it.”

“Nobody outside Romney’s inner circle knows anything, and they aren’t talking. The rest of us are left to try to read tea leaves and photo-ops. Naturally, we misinterpret many of the signals because we lack context.”

Few, he said, expected Richard Nixon to tap Maryland Gov. Spiro Agnew in 1968, George McGovern to select (and later replace) Sen. Thomas Eagleton of Missouri in 1972, or Walter Mondale to pick Rep. Geraldine Ferraro of New York in 1984.

George H.W. Bush also surprised people when he named Sen. Dan Quayle of Indiana as his right-hand man in 1988. His son, George W. Bush, also turned some heads when he brought former Defense Secretary Dick Cheney on board in 2000.

“It’s impossible to get inside the head of a presidential nominee,” Mr. Sabato said. “But we’ll all die trying.”