If you're curious why the candidates were tripping over themselves to out-praise Marco Rubio, Florida's Republican junior senator, at the last debate, look no further than the political market Intrade, where Rubio is in first place to be second fiddle with a 24 percent chance of being the eventual winner's running mate. (Meanwhile Joe Biden is the overwhelming favorite to remain Obama's choice.)
But who gets the would-be VP nod depends greatly on who is the nominee. As Newt Gingrich's odds of winning have spiked and dissipated twice in the last two months, the market for vice presidential candidates has reacted. Because the movement happened over a fairly short time period -- I analyzed the past 90 days -- and because not much else seems to have occurred to impact the veepstakes picture during that time, we can guess that most of the changes in the VP market are driven by the shifting fates of Romney and Gingrich at the top. With this assumption, we can compute estimates of which pairings are most likely.
If Mitt Romney is the Republican nominee, my model estimates that he is 25 percent likely to pick Chris Christie as his running mate, a popular moderate governor from New Jersey who himself flirted with running for president before strongly endorsing Romney. (This in spite of the fact that you'd have two Northeasterners on the ticket.) The market puts Christie's overall chance of being the VP of any Republican nominee at only 14 percent, but because his odds tend to rise in tandem with Romney's, my model boosts his chances to 25 percent in the scenario where Romney is the nominee. Rubio is a close second to be Romney's right-hand man at 22 percent. Rubio's VP odds actually drop whenever Romney's go up (they are anti-correlated), but because Rubio's such a likely overall pick, he's still the second-most likely Romney pairing. Rubio so far hasn't endorsed a presidential candidate and has repeatedly said he's not interested in the VP job. No other candidate rises above single digits as Mitt's pick for a-heartbeat-away.