By: Gwen Ifill

With the Republican primary campaign approaching its end, and more than two weeks before the next voting, there is immense temptation to begin speculating about running mates.

I will resist. That seems the respectful thing to do when there are three other candidates who insist they are still in the race for the nomination.

I will resist wondering why Sen. Marco Rubio of Florida -- at the top of almost every list -- thought it was a good idea to tweet this week about how much he loves wild child Nicki Minaj's music. Does he know she was escorted to this year's Grammy Awards by a man dressed as the pope?

I will resist freaking out over how much Rep. Paul Ryan, R-Wis., looks like Mitt Romney's unacknowledged sixth son.

I will not grill my relatives in Albuquerque about what they think of their governor, Susana Martinez. ("It's humbling, but I'm not interested," she said this week.)

And I will not dig out all the stories about how Meg Whitman spent a whopping $163 million to lose the California governor's race to Jerry Brown in 2010. That's $54 for every vote she won, and she got beat by a million votes. Brown's expenditures added up to $6.25 per vote.

Yet she's probably the only vice presidential possibility who is not being coy about wanting the job. "I'd be happy to do almost anything he wants me to do," she said last year. "So we'll see."

Hmmm. Who else? Rob Portman of Ohio? Nice fellow. Chris Christie of New Jersey? Why not? Bob McDonnell of Virginia? Great hair. Kelly Ayotte? The New Hampshire senator looked pretty at home on the Romney campaign trail this winter.

For the 91 Republican insiders surveyed by National Journal in this week's issue, Rubio is the top choice, followed by Portman, Ryan, Christie and -- at 2 percent -- Louisiana Gov. Bobby Jindal.

We stand at the precipice of a rabbit hole that could well consume our entire summer. But if I've learned nothing else from years of quadrennial running mate speculation, it's that we are usually wrong.

This is how the veepstakes goes. It begins with a round of stories of how the incumbent is going to drop his second-in command. It took months before President Obama could convince everyone that Joe Biden was going nowhere.

Part of this was driven by diehard Hillary Clinton fans who never got over 2008. And part of it came from Biden's ability to periodically say something unfortunate. In any case, the campaign printed up a batch of "Obama-Biden 2012" bumper stickers, and that pretty much shut everybody up.

Dick Cheney, Al Gore and Dan Quayle also fell victim to rumors they would be dumped. Yet only nine vice presidents have been tossed from the ticket, the last one Henry Wallace in 1944. The first, Aaron Burr, was understandably sidelined after he shot and killed the secretary of the Treasury in a duel.

So with Biden securely in place and already out on the campaign trail, all eyes turn to Mitt Romney.

But mine will not. I will not scour statehouses for dark horse governors. I will not rate potential candidates by their ethnicity, geographic desirability or love of Bruce Springsteen. And I will not book a flight to Wasilla.

Do you hear that Jeb? Rick? Newt? Bobby? If someone is on the other line, it won't be me.

I will be off somewhere covering a duel.

Gwen's Take is cross-posted with the website of Washington Week, which airs Friday night on many PBS stations. Check your local listings.