For some time it seemed that the Iowa caucuses would be unimportant in the 2012 Republican presidential primary. Rep. Michele Bachmann (R-Minn.), especially after her big win at the Ames straw poll, appeared to be a shoo-in. Burned by his loss in 2008, Mitt Romney was determined not to expend much effort there. But a lot has changed since August.

A new NBC-Marist poll highlights the dangers for both Bachmann and Texas Gov. Rick Perry. Romney is leading among caucus-goers with 23 percent, followed by Herman Cain at 20 percent. Far behind is Rep. Ron Paul (R-Tex.) at 11 percent. More than a dozen points behind Romney, Bachmann and Perry each draw 10 percent. Much can happen before January, and unless it does Bachmann and Perry could very well find that their presidential runs end in Iowa.

Bachmann, the Iowa native as she reminds us frequently, has put in enormous time and resources in Iowa. She is running on fumes — her funds are quickly running out. If she can’t win in Iowa she is unlikely to win elsewhere, and it would make little sense for her to stay in the race.

Likewise, the once-formidable Perry has two realistic openings in the early contests — Iowa and South Carolina. A finish in the caucuses in the back in the pack would confirm his second-tier status and leave him vulnerable to wipe-outs in New Hampshire and Nevada. He, too, could find it difficult to fight on.

Conversely, a Romney win might effectively end the race. If he can win there and coast in New Hampshire (where he leads by a wide margin now), he’ll have momentum to win in Nevada. South Carolina may be a stretch, but Florida could well seal the nomination for him.

As for Cain, he has now raised expectations for a strong showing in Iowa. However, he’s not spent significant time there and lacks a ground game to get voters to the caucuses. A close second or an upset win would cement his status as the not-Romney option; a worse finish could well take the wind out of his sails and raise doubts as to his viability as a serious contender.

Iowa doesn’t often pick the winner in the GOP presidential primary. (Ask Mike Huckabee if you doubt that.) But it sure can eliminate some contenders. In the 2012 race, Perry and Bachmann are going to have to go into overdrive, reestablish their credibility as credible nominees and shore up support among social conservatives if they are to avoid defeat and an early end to their presidential aspirations. They might consider focusing all their energies on the caucuses; if they don’t do well there, none of the other states will matter much.