By Candy Crowley, CNN Chief Political Correspondent

Washington (CNN) - Mitt Romney thinks a Wisconsin/Maryland/D.C. sweep Tuesday night will set him sailing to the nomination long before the August Republican convention.

Still, he's not about to own it.

Asked at a diner in Fond du Lac, Wisconsin whether he had made a vice presidential pick, Romney said no. "I'm not presumptuous enough because I'm not the nominee yet."

Rest assured someone inside Camp Romney is thinking about vice presidential picks. The candidate, though, follows a long line of almost-nominees who do not want to be caught publicly musing about a No. 2.

There is no such reticence in the rest of political world, where it is never too early to rush the season with a quick round of veepstakes.

Among the most frequently mentioned vice presidential possibilities:

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