Former Massachusetts governor Mitt Romney (R) has yet to clinch the Republican presidential nomination, but that hasn’t stopped the vice-presidential speculation from already kicking into overdrive.

Will it be Sen. Marco Rubio (R-Fla.)? Sen. Rob Portman (R-Ohio)? House Budget Committee Chairman Paul Ryan (R-Wis.)?

There’s certain to be plenty of guesswork about the veepstakes from here to the Tampa convention this summer, but a bigger question looms over all the speculation: Does a candidate’s choice of running mate make a difference in the fall?

Today’s Trail Mix video takes a look: