The race is close, with Braley's once-substantial lead having either shrunk or vanished depending on which campaign you talk to. It has been a prime opportunity for Republicans to gain one of the six seats they need to recapture Senate control ever since long-time Democratic Sen. Tom Harkin announced that he wouldn't seek re-election.
Braley boasts considerable experience and a solid political profile after eight years in the House. The state has drifted Democratic in recent presidential elections—President Barack Obama carried it in both 2008 and 2012.
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But Ernst, a state senator and Iraq War veteran, has made effective use of her connection to the state's agriculture character. She burst to prominence within the Republican primary field earlier this year with a TV ad in which she boasted of her experience castrating hogs and vowed to "make 'em squeal" in Washington by cutting spending.
The race presents challenging cross-currents for both candidates. The electorate here includes more Republicans than Democrats, which means Braley must win a majority of independents to prevail. As elsewhere, women voters represent a key swing constituency that has often leaned Democratic. But Ernst has the potential to generate excitement from the fact that, if elected, she would be Iowa's first-ever female senator.
Braley, who recently shook up his campaign team, hopes to erode Ernst's support in the homestretch. He will cast her as at odds with average Iowans on the minimum wage and Social Security and at odds with Iowa business because of her philosophic objection to government interventions in the economy, one of which helps Iowa farmers by requiring corn-based ethanol to be used in gasoline.
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Ernst vows to support the "Renewable Fuel Standard" requiring ethanol use so long as other government interventions benefit other industries elsewhere. On issues such as Social Security, she touts her willingness to confront rather than duck tough issues, while protecting benefits for current recipients from any transition to a new system. And her campaign counts on portraying Braley as having grown out of touch with the culture of the state in a year when Washington and the Democratic president are especially unpopular.
Both sides expect this fight between two styles of class warfare—economic versus cultural—to remain tight until November, just like the national battle for Senate control.
—By CNBC's John Harwood