Nearly all political gurus a year or even a few months ago, if asked about the prospective campaigns of former Minnesota governor Tim Pawlenty and Rep. Michele Bachmann (R- Minn.), would have picked the ex-governor as the more viable of the two contenders. But politics is about performance and Pawlenty has underperformed while Bachmann, benefiting from low expectations, is the race’s overachiever.

You can see it in the polls, in the money race (although Bachmann has yet to release her second-quarter fundraising totals) and in their rhetoric. As to the latter, Pawlenty sounded increasingly defensive in Iowa yesterday:

“Iowa has done a remarkable job in maintaining, preserving its first-in-the-nation caucus status, but we want to make sure it’s not just first, but it’s also right in selecting and predicting the nominee and the ultimate selection for president,” Pawlenty says. “I’m just trying to urge them to consider the whole process, not just the first step.”

Pawlenty, the former governor of Minnesota, spoke earlier this afternoon to about 75 people at the Surf Ballroom in Clear Lake. Pawlenty told reporters his comments were not directed at competitor Michele Bachmann, a fellow Minnesotan.

“No, it wasn’t directed at anybody in particular,” Pawlenty said. “I was just trying to make the general point that Iowa plays such a prominent role in the selection process so early, that (Iowans) can make or break campaigns.”

Maybe it wasn’t directed at Bachmann, but she certainly must be on his his mind. And she should be.

If Pawlenty bombs in the Ames straw poll and comes in far behind Bachmann in the Iowa caucuses next year, he’s done. In fact, given his money situation, a poor Ames showing may effectively knock him out of the top tier and leave him permanently in single digits in the polls.

The punditocracy is shocked, if not aghast, that Bachmann is on the rise while that “nice” man from Minnesota, to put it mildly, has not yet caught on with the GOP electorate or donors. But then they were shocked by her debate performance and are shocked by her un-Palin-like proficiency on a variety of topics, including conservative economic theorists. (The sure sign she is becoming formidable? A fixation on her gaffes, which as of yet are a fraction of the number racked up by candidate Barack Obama.) The explanation for the contrasting fortunes of these two candidates is three-fold: instincts, ideology and independence.

Bachmann is a force to be reckoned with because she combines smarts with near-perfect political pitch for the Tea Party contingent. Without Sarah Palin’s obsession with victimology (most especially toward the press), she taps into the Tea Partyers’ anger toward the governing class. She plainly has a penchant for sharp barbs (usually directed at the president) and a keen appreciation for the conservative electorate’s mood. Most important, she saw an opening for her own candidacy when virtually no one else did. She is promising to change the party and the country; Pawlenty seems to be running on his experience and general election appeal. (Think Obama vs. Hillary Clinton in 2008.)

As for ideology, there’s virtually no room on Bachmann’s right. She opposed TARP, the stimulus, ObamaCare and cap-and-trade. Meanwhile, Pawlenty faces continued skepticism over aspects of his record as governor. Club for Growth, in its white paper on Pawlenty, concluded:

Pawlenty deserves tremendous praise for keeping Minnesota’s spending growth remarkably low. For this, and for his consistent stances on school choice, tort reform, and political free speech, he deserves credit – while his record on health care and entitlement spending is mixed. However, Pawlenty has some simply inexcusable tax hikes in his record, and he made a mistake by taking no clear position on the 2008 Legacy Amendment. His tacit support for bailouts, more job-choking regulations, and various tariffs make it difficult for us to identify his core ideological identity. His support of things like mandatory vegetable oil in gasoline, cap and trade, and a statewide smoking ban make him sound overly eager to support big government proposals to address policy fads of the day.

Of Bachmann, the Club for Growth writes: “With very few exceptions, Congresswoman Bachmann has supported pro-growth policies throughout her career. She especially deserves praise for her consistent defense of school choice. After reviewing her record, we are confident that Congresswoman Bachmann would be a pro-growth President.”

And finally, Bachmann can hardly be accused of being cautious, tentative or over-managed. If anything, the concern is her lack of first-rate advisers and her willingness to stir up controversy. Pawlenty is so scripted these days he’s beginning to seem like an ideal candidate — for the vice presidency. In short, she’s standing out and he’s blending into the field of contenders.

None of this is to say that Pawlenty can’t win the nomination or that Bachmann will win it. But there are good reasons why he’s in trouble and she’s now Mitt Romney's biggest threat. She is, you know.