WASHINGTON -- Democratic Senate candidate Heidi Heitkamp is walking through neat rows of soybeans in blue jeans and a fleece jacket, with a silo and grain bins visible in the background, talking about the need to put North Dakota farmers ahead of partisanship.
That TV ad, which debuted Sept. 13, is the latest in a series of appeals to the state's rural voters. She often reminds them that the Republican-led House has failed to even vote on the every-five-year agriculture policy bill that funds subsidies for farmers. She credits that pitch with helping nudge the North Dakota Senate race from a probable Republican pickup to a tossup.
"Agriculture is still king in this state," Ms. Heitkamp, who is challenging Republican Rep. Rick Berg in the race to succeed retiring Democratic Sen. Kent Conrad, said in an email. "You can't represent North Dakota in the United States Senate without fully representing our farmers and ranchers."
With Democrats holding a slim majority in the Senate, both national parties have shifted resources to North Dakota, a state with a booming economy and lowest-in-the-nation unemployment rate of 3 percent. It is among a handful of rural states where Democrats see opportunity in the stalled farm bill, a version of which passed the Senate.
"If you had asked Republicans a year ago, they would have told you North Dakota would be over by Labor Day, and it's not," Jennifer Duffy, who monitors Senate races for Cook Political Report, said in an interview. Democrats "are still in it, and they're still fighting."
The failure of the House to pass a farm bill is not the only reason, she said. It has contributed to a narrative of Washington's failure, something Ms. Heitkamp is using to her advantage in her campaign against a House member, Ms. Duffy said.
Other Senate campaigns where farm issues could become a factor include in Indiana, where Democratic Rep. Joe Donnelly is running against Richard Mourdock, the Tea Party favorite who knocked off incumbent Richard Lugar in a Republican primary, and in Wisconsin, where former Republican Gov. Tommy Thompson is running against Democratic Rep. Tammy Baldwin for the seat vacated by Herb Kohl.
The stalled farm bill could influence some House races, though polls show that chamber will probably remain under Republican control. It is in the Senate, where Democrats hold 51 seats, that a handful of races could tip the balance of power. Republicans have 47 and need three more to control the chamber. Two senators are independents who caucus with Democrats.
Inaction on the farm bill may weaken the GOP Senate effort in rural, conservative states such as North Dakota and Montana that are out of reach for Democrats at the presidential leve, yet still attainable in congressional races, said political science professor Steffen Schmidt at Iowa State University in Ames.
"In some states, it will be a big issue," Mr. Schmidt said in an interview, noting that divisions in the House between rural lawmakers who support subsidies and budget hawks within the Republican caucus have made it difficult for that chamber to pass a bill. "The Democrats could make a lot of hay because it's the Republicans that are blocking passage."
Republicans have shifted campaign spending to North Dakota, some of it from Missouri, where they've canceled money earmarked for the Senate campaign of Rep. Todd Akin, whose comments about "legitimate" rape have cost him support, Ms. Duffy said.
Agriculture issues are prominent in campaign ads in the Montana race, where polls show Republican Rep. Denny Rehberg leading incumbent Democratic Sen. Jon Tester by 4 percentage points. That is down from 10 points in May. "Jon Tester's ads all have combines in them," Ms. Duffy said.
Lack of a farm bill has "become a very salient issue in a lot of key battleground races, and it's highlighted the intransigence and ineffectiveness of House Republicans like Denny Rehberg and Rick Berg and put their misplaced priorities front and center," said Matt Canter, the Democratic Senatorial Campaign Committee communications director.
In Senate campaigns, particularly in rural states, candidates can localize their races around issues such as agriculture, Mr. Canter said. That enables Democrats such as Ms. Heitkamp and Mr. Tester to woo voters who might vote Republican in the presidential race, he said.
Republican presidential candidate Mitt Romney may easily win North Dakota and Montana, "but that's not providing a lot of solace to Rick Berg and Danny Rehberg right now," Mr. Canter said.
Emails and calls to the National Republican Senatorial Committee were not returned.
The farm bill's delay "makes a huge difference to farm-state Republicans. Just look at the members who've been speaking publicly," House Agriculture Committee Chairman Frank Lucas, R-Okla., said in an interview.
A version of the bill, which would reauthorize subsidies for growers of corn, cotton and other crops, has been approved by the Senate. The House Republican leadership did not schedule a vote before Congress recessed for the election, so no bill will pass before the current law expires Sept. 30.
House Majority Whip Kevin McCarthy, R-Calif., earlier this month said the House leadership hopes to get a farm bill passed by the end of the month.
"I am disappointed that they haven't scheduled this for a vote," said Rep. Kristi Noem, R-S.D. "Frankly, I take my direction from the people of South Dakota."