If Mitt Romney wins the GOP nomination, he will then have to choose a vice-presidential candidate to run as his #2 on the ticket. That prospect could be terrifying for Romney.
The American Prospect's Paul Waldman says the choice of a V. P. candidate usually solves a problem for a campaign - shoring up a geographical weakness or to balance a ticket ideologically.
Romney's problem, according to Waldman, is that the Republican base doesn't much like him or trust him as a conservative. But, if he makes a veep pick to placate them, it could turn off moderate voters in November's general election.
Which makes it important for Mitt, in his first major decision as the party's nominee, to make a pick that gets conservatives excited about the fall campaign and assures them that they'll have a representative in his White House. But the extended primary race has had a simultaneous effect on independent voters: the more they've seen Mitt pander to the Republican base, the more they'll need reassurance that he's not some kind of contraception-banning, foreigner-bombing, rich-folks-tax-cutting extremist. It would seem impossible for Mitt to offer simultaneous reassurance to both groups.
It's important to remember, as he approaches this decision, that in his political life Romney seems governed by fear to a degree even greater than most politicians. Some politicians are risk-takers, like John McCain (his most notable risk, of course, being a certain Alaska governor). But most are cautious, Mitt unusually so. Is there a VP candidate out there who looks to the conservatives like a hard-core, "one of us" kind of figure, but also assures independents that Romney is a moderate? I doubt it. So I imagine this choice is just going to be terrifying for him.