But it has joined a collection of second-tier opportunities, a list that includes fellow purple-state battlegrounds Colorado, New Hampshire, and Michigan—each put into play by viable candidates and a favorable political climate for the GOP. And, like them, the Hawkeye State could eventually become an irreplaceable part of the party's plan to take the Senate should it stumble elsewhere.

If Republicans do go on to win in Iowa, they'll trace their victory back to the final week of March. It was then that a video leaked of Braley talking to a group of Democratic donors, urging them to prevent Republicans from retaking the Senate and letting fellow Iowa lawmaker Chuck Grassley take the gavel of the Senate Judiciary Committee.

"You might have a farmer from Iowa who never went to law school, never practiced law, serving as next chair of Senate Judiciary Committee," he said. "Because if Democrats lose the majority, Chuck Grassley will be the next chair of the Senate Judiciary Committee."

The comment went down as one of the worst gaffes of the still-young midterm season, and Braley apologized within hours.

But to Republicans, it provided the frame for Ernst's entire candidacy: a small-time Iowa farmer (and veteran) taking on a condescending liberal more at home on either coast. (It also explains why most, if not all, Republican operatives preferred that Ernst win the party's nomination over the millionaire Mark Jacobs, who could self-fund but would struggle to depict himself as a blue-collar champion.) That's a potentially potent argument in a state that's not just farm-heavy, but also one in which blue-collar white voters made up 56 percent of the electorate in 2010.

"It provides a strong contrast that I think a lot of Republicans in D.C. are anxious to have," said Matt Strawn, a former chairman of the Iowa GOP. "Someone who comes from rural Iowa, who has a nonpolitician feel about her, running against an incumbent member of Congress."

That March week was also a springboard for Ernst's own campaign, when a soon-to-be viral TV ad about her experience castrating hogs made national news. The ad was mocked by late-night comedians, but it generated the kind of attention she needed to separate herself from her opponents and gain the attention of national groups. Ernst received the endorsements of a wide variety of people and groups, including Mitt Romney, Sarah Palin, and the Senate Conservatives Fund.

That attention could benefit her again this summer, when she'll need to replenish her campaign coffers.

"I think you could also see a lot of interest shift from Michigan to Iowa," said one Republican strategist with an eye on the national picture, referring to another midterm battleground where the presumed GOP nominee, Terri Lynn Land, has struggled to answer reporters' basic questions.