Dan Koeck for The New York TimesHeidi Heitkamp, the Democratic Senate candidate in North Dakota, visited Perry Benton of Minot while campaigning last week. MINOT, N.D. — Heidi Heitkamp, a Democratic Senate candidate, called Leonard Rademacher a few weeks ago looking for his vote, but Mr. Rademacher, a 74-year-old retiree, was feeling ill, so Ms. Heitkamp called him back. A one-stop destination for the latest political news — from The Times and other top sources. Plus opinion, polls, campaign data and video. Representative Rick Berg, the Republican candidate, campaigning at a business in Fargo. “I said: ‘Heidi, save your breath. I’m voting for you,’ ” Mr. Rademacher recalled, marveling at her personal attention. “I don’t necessarily agree with her, but I trust her.” Gary Volk backed Ms. Heitkamp, a former state attorney general, after she sat for four hours on a slab of concrete next to what was once his house, listening to his struggles to recover from catastrophic flooding last year. Larry Windus’s mind was made up by an encounter with her opponent, Representative Rick Berg, a Republican, that ended with the candidate turning his back on him. “He’s not very personable,” said Mr. Windus, 55, a dishwasher at Charlie’s Main Street Cafe here. Senate Republicans considered the state in their column when Senator Kent Conrad, a veteran Democrat, announced his retirement last year. But with shoe leather, calibrated attacks and likability — an intangible that goes far in North Dakota — Ms. Heitkamp has made this a real fight. Though North Dakota is deeply conservative and is on no one’s presidential map as a question mark, this race could be one of the biggest surprises of the 2012 contests. And, like all close races this year, it could help decide control of the Senate. Even the National Republican Senatorial Committee conceded in its most recent attack ad here that Ms. Heitkamp is making headway. “Heidi Heitkamp: You might like her, but on the issues she’s wrong for North Dakota,” it said. The contest — the state’s first competitive one since 1986 and probably its nastiest in modern history — features two very different politicians with very different styles: the rumpled Democrat against the well-turned-out Republican, the longtime denizen of state government against the affluent businessman. Ms. Heitkamp hugs her way through a room. Mr. Berg approached a table of women in Fargo on Wednesday and then sheepishly backed off, saying: “We won’t bug you. We’ll just keep going.” Ms. Heitkamp sees the Senate as a platform to help North Dakotans, with air service, veterans’ health care, flood control, wind energy production and agricultural assistance. Mr. Berg wants North Dakota to help the nation. “We’ve gone from a state that has kind of been in the bottom half of the country in terms of our economics and business to really the envy of the nation,” he said at Butler Industries, a heavy-equipment dealer in Fargo that is booming along with North Dakota’s energy and agriculture sectors. “My passion is taking what we’ve done in North Dakota — if you will, the North Dakota way — and applying it nationally. If we do that, we can reignite America’s economic engine.” Ms. Heitkamp, surveying the slow rebuilding after the flooding in Minot, offered a different sentiment. “You stand here, and you say this should not be,” she said. In short, the campaign is a contest between North Dakota Nice and the national strategy of the Republican Party. “Everyone’s pretty likable,” Mr. Berg said with a shrug. “The issue is not about a personality contest. This whole thing kind of boils down to, do you want someone who’s going to fight against President Obama.” Tight Senate races in Arizona, Connecticut, Indiana, Massachusetts and North Dakota all feature one candidate who must count on voters going one way in the presidential race and another down the ballot to prevail. But in North Dakota, voters have been splitting their tickets for decades. The seat up for grabs here has been in Democratic hands for 52 years. Only once in that span, in 1964, has the state voted for a Democratic presidential candidate.