Rep. Michele Bachmann's August victory in the Ames Straw Poll was supposed to propel her campaign forward, but she's only slumping deeper in the polls. In a new Gallup/USA Today national poll, only 5 percent of Republicans listed her as their first choice, down from 10 percent in August. Bachmann was once hailed as a top-tier candidate for the GOP nomination. What went wrong? Here are four theories:

1. Perry stole her thunder
Texas Gov. Rick Perry has eclipsed Bachmann as the conservative's conservative, says Pete Spiliakos at First Things. She was top tier until he entered the race on August 13 — now she's "down there with Newt Gingrich and Herman Cain." And her path back to the top gets harder every day: "She not only has to peel off Perry's more conservative and populist supporters," but make sure they go from Perry's camp to hers, "rather than dividing between herself, Ron Paul and [Rick] Santorum."

2. And her anti-Perry fans are jumping to Romney
While Bachmann falls, Mitt Romney is chipping away at Perry's lead, says Neil Stevens at RedState. Romney was behind Perry by 12 points in August, but now he's just 7 points back. Arguably, his gain is Bachmann's loss. As Bachmann started looking increasingly like a longshot, a big chunk of disillusioned Bachmann supporters may have "jumped on board the anyone-but-Perry train." Even some pro-Bachmann Tea Partiers may be settling for Romney as "a second choice." One reason: Romney's performance in the last two debates boosted his support among conservatives.

3. She isn't equipped for a national campaign
The Minnesotan isn't trying to make a splash nationally, says her former campaign manager, veteran GOP strategist Ed Rollins, as quoted by MSNBC. "She doesn't have the ability or resources" to go head to head with frontrunners Perry and Romney, who have enough campaign cash to criss-cross the nation for months. Bachmann is staking her entire campaign on winning the Iowa caucuses in early 2012 — and her focus on the Hawkeye State means Bachmann is all but ignoring South Carolina, Florida, Arizona, and other key states.

4. Bachmann is sinking herself with gaffes
The Minnesota congresswoman was the "darling of the Republican primary," says the Red Dog Report, but her "gaffes and mistakes" have made it hard for voters to see her as presidential material. Her claim that the HPV vaccine Gardasil causes "retardation" — despite a mountain of evidence to the contrary — was just the tip of the iceberg. This week in Iowa, she railed against government grants to businesses — while touring a manufacturer that gets 80 percent of its revenue from Washington. "It may be time for her to lick her wounds and exit the GOP presidential primary."