Tim Pawlenty dropped out of the Republican presidential race on Sunday after a disappointing third-place finish in the Iowa straw poll. The former Minnesota governor had invested heavily in Iowa, and said he needed a strong showing to attract the campaign donations necessary to keep going. Pawlenty, who touted his success as a Republican governor in a Democratic state, was once considered a potential mainstream GOP alternative to frontrunner Mitt Romney. How will his departure shake up the contest for the Republican nomination? Here are four theories:

1. Michele Bachmann gets to polish her record
Just a few days ago, Pawlenty had dropped his nice-guy strategy and was dismissing Bachmann's Congressional record as non-existent, says Jed Lewison at Daily Kos. "And now, after taking a drubbing [in Iowa], what is he saying? 'I think she's qualified to be president.'" Winning "the coveted 'you're qualified' endorsement from none other than Tim Pawlenty himself" certainly won't hurt Bachmann's campaign.

2. Mitt Romney is now the mainstream's only choice
"Pawlenty's withdrawal leaves Mitt Romney as the only serious candidate who is mainstream in both policy views and persona," says John Hinderaker at Power Line. Romney might still fall victim to "the rebellious mood" that knocked down Pawlenty, but it's increasingly apparent that Republicans want to make the 2012 race about President Obama's record on the economy. And "Romney looks like the candidate best positioned to achieve that strategic goal."

3. This opens the door for Rick Perry
This doesn't help Romney — he and Pawlenty were contending for the "grown-up vote," so anyone who liked Pawlenty had "already rejected Mitt for whatever reason," says John Deeth at the Des Moines Register. But it does help the newest member of the GOP field — Rick Perry. The Texas governor made his first stop in Iowa as a candidate just as Pawlenty's withdrawal left "13 percent of the straw poll vote and a decent organization shaken loose from the moorings." That's a "good list of phone calls" for Perry to make as he tries to make up for lost time.

4. Tea Partiers have pushed aside "Sam's Club Republicans"
Pawlenty's departure won't have a huge impact on the race — that's why he's giving up, says Ben Smith at Politico. But it does mark "a failure of the Sam's Club conservative brand [that] Pawlenty sought, at times, to personify." Pawlenty's Minnesota-nice, populist conservatism with a blue-collar edge would have gone over better if the base had been interested in "tacking to the center." But the small-government, Tea Party conservatives who are fueling the campaigns of Bachmann and Paul are "interested in rolling government back, not reshaping it."