Political campaigns are getting started earlier than ever these days, so why should the vice presidential vetting process be any different?

All of the top early contenders for the Republican vice presidential nomination have seen their records put under a microscope in recent weeks.

Sen. Marco Rubio (R-Fla.) has been the target of some tough stories for months now, ranging from his claims about his parents’ immigration from Cuba to his personal finances (stories, we should note, that have largely only led conservatives to rally around Rubio).

More recently, New Jersey Gov. Chris Christie and Virginia Gov. Bob McDonnell have also come under the national microscope.

Rubio, Christie and McDonnell are the three most-likely VP nominees, according to InTrade, and all three are getting the running-mate treatment already.

Christie, who is already a national figure for the GOP, was recently sent a gay marriage bill that passed in the Democratic-led state legislature. He vetoed it on Friday, a move that may help his national prospects but might not be the best call in blue-leaning New Jersey, where Christie faces a reelection campaign next year.

Also in recent weeks, the newly Republican-controlled Virginia state legislature has pushed along a couple of abortion-related bills that could put McDonnell in a tough spot, choosing between the conservative base and a more tenable position if he wants to be the Republican vice presidential nominee.

McDonnell may be in the toughest spot of anybody right now if the bills reach his desk.

He so far hasn’t taken a position on either a “personhood” bill that would define a fertilized egg as a person or on a bill that would require a transvaginal ultrasound before a woman can get an abortion.

Thus far, his office hasn’t committed to signing the bills and sounds downright skeptical about the “personhood” bill.

“He has significant concerns that this proposed legislation has major constitutional issues and may not withstand court scrutiny,” McDonnell’s spokesman has said.

In truth, there’s not a good option here for McDonnell.

A similar “personhood” measure failed on the ballot in heavily conservative Mississippi in November, so it’s not like it’s an easy call, even for a social conservative like McDonnell. By signing the bill, he may appeal to the GOP’s socially conservative base at the expense of independents, and by vetoing it, he would undoubtedly cause problems for himself on the right.

Some right-leaning bloggers are already suggesting McDonnell faces a choice between conservatism and his national ambitions.

The ultrasound bill appears to be a similar circumstance, in which there really isn’t a great position for McDonnell to take. The issue was the subject of a joke on “Saturday Night Live” this week — raising its national prominence to a level that McDonnell would probably rather not deal with as he campaigns for Mitt Romney in Michigan this week.

Democrats are gleeful at the idea that McDonnell is in a tough spot, and Republicans also suspect Democrats are behind the early scrutiny of Rubio’s record.

Whether that’s true or not, it should be noted that the opposition has also gone after some of the other top vice presidential contenders, including Rep. Paul Ryan (R-Wis.) — whose budget Democrats have repeatedly demonized — Sarah Palin and, of course, Rick Santorum, who is ranked by InTrade as the fourth most-likely vice presidential candidate.

It’s a solid strategy. We saw in 2008 with Palin how a vice presidential candidate can very much become the issue in a presidential campaign, provided that there is some compelling stuff to talk about.

And make no mistake: The auditions for vice president have been going on for months now.