MINNEAPOLIS — With two Democrats in tight re-election bids, voters could dramatically change the complexion of the state’s congressional delegation today.

Rep. Rick Nolan fought to keep his northeastern Minnesota swing district against newcomer Republican Stewart Mills in a U.S. House race that’s among the most expensive nationally. And in northwestern Minnesota, longtime Democratic Rep. Collin Peterson became a surprise target for national Republicans’ attack ads, putting his typically easy re-election in question.

The state’s only open congressional seat — being vacated by retiring GOP Rep. Michele Bachmann — is weighted heavily in favor of ex- Republican gubernatorial candidate Tom Emmer. Elsewhere, Democrats in the Twin Cities metro and Republicans in suburban districts are expected to cruise to re-election.

Mills, a 42-year-old scion of the Fleet Farm chain of stores, hoped to capitalize on the 8th District’s changing political face. He weathered attack ads from Democratic groups targeting his personal wealth — and his chin-length hair — in a race that topped the $10 million mark for outside spending.

Mills called for a “flatter, fairer” tax code and criticized Nolan for supporting President Barack Obama’s health care overhaul, as well as votes to ban assault weapons and on other gun control measures. Nolan, 70, defended his stance on guns, saying he doesn’t need an assault rifle to go hunting.

Seeking a second term in his second stint in Congress — he also served in the House in the 1970s and early ’80s — Nolan played up a middle-class ethos in the waning days of his campaign. He, too, was the subject of millions of dollars of attack ads from outside groups.

Peterson, who has mostly coasted through re-elections during his 12 terms, got a first taste of outside money in the massive 7th District.

Peterson faced pressure from Republican state Sen. Torrey Westrom, and the GOP took notice. The National Republican Congressional Committee seized on Peterson’s travel expenses from car leases and his personal plane, and spent millions on attack ads to try to paint the conservative Democrat as out-of-touch.

Peterson, 70, played up his agricultural expertise and stewardship of the 2014 farm bill to shore up support in the conservative-leaning 7th District.

Westrom, a 41-year-old attorney who has spent nearly two decades in the state Legislature, called for new voices in Washington to break gridlock in Congress.