Just when it looked like U.S. Republicans were marching to a Senate majority in next month's midterm elections, an obscure race in the state of Kansas blew up in their faces and may prevent the GOP capturing that longed-for lock on both houses of Congress.

Republican Senator Pat Roberts was supposed to be a shoo-in for re-election – the man's been in Congress since 1981 and the last time Kansans sent anyone but a Republican to the Senate, Herbert Hoover was president.

Thanks, however, to an effective campaign by an unknown businessman running as an independent, Mr. Roberts, 78, could be the only Republican senator to go down to defeat Nov. 4. The Democrats withdrew their candidate from the ballot to leave the field open to the independent, Greg Orman, and not even a parade of Republican stars nor all the money the right-wing Koch brothers are spending on TV attack ads seem able to stop him.

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Since late September the likes of John McCain, 91-year-old Bob Dole in a wheelchair, and Sarah Palin, have stumped for Sen. Roberts. Kentucky Sen. Rand Paul, a likely candidate for president in 2016, is scheduled to make numerous appearances for the Roberts campaign this weekend.

But Mr. Orman has convinced a great many Kansans that Sen. Roberts's longevity in Washington is typical of the problem afflicting national government, and that such Washington figures only accentuate the problem. Polls continue to show Mr. Orman with an average lead of almost 5 percentage points.

That a Republican should fall in Kansas is surprising. That he should lose to the rarest of political characters – an independent – is unheard of and reflects a genuine disenchantment with traditional party politics.

For his part, Mr. Orman has said that if elected, he'll caucus with whatever party holds a "clear majority" in the Senate. But if there are 50 Republicans and 49 Democrats, he can swing control to either party, since the Democratic vice-president, Joe Biden, would cast a deciding vote in the event of a tie.

The man is serious about his bipartisan credentials. When it became clear he had a real chance of winning, Mr. Orman hired five veteran campaign organizers with national experience: three had worked with Democratic candidates and two with Republicans.

At the Orman for Senate headquarters in this Kansas City suburb – a modest storefront operation nestled between a Tae Kwon Do studio and a muscle and joint clinic – the candidate's Princeton yearbook is open at the page describing the college student as a young Republican. On the wall above it a framed 1970s photo has the Orman youngsters with their divorced mom posing with former Democratic vice-president Hubert Humphrey, for whom the mother's father worked.

A print of a famous John Steuart Curry mural also is pinned to the wall. It's the only art in the room. The picture, Tragic Prelude, depicts the radical abolitionist John Brown, with a Bible in his left hand and a rifle in his right, stepping over corpses as he leads a charge against pro-slavery forces along the Kansas-Missouri border in the 1850s lead up to the Civil War. The original mural is in the state capitol in Topeka.

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Both Republicans and Democrats are proud of the state's anti-slavery past and while many identify still with the Bible and the gun, this also is the state where a 1954 lawsuit brought against the Topeka school system – Brown versus Board of Education – led to a landmark U.S. Supreme Court decision that desegregated schools.

Now, however, it is Kansas's powerful anti-abortion movement that sees itself as today's abolitionists and wields considerable political influence, especially among Republicans in Wichita and the southern half of the state.

Sen. Roberts had once been known for his moderate views and good-humoured accommodating nature on a wide range of issues. But with the growing clout of the anti-abortion movement, and of the right-wing Tea Party with its less-government less-taxes agenda, the senator tacked hard to the right. The Heritage Foundation ranks him as the third most conservative member of the Senate and he is endorsed by the National Rifle Association and the National Right to Life movement.

Ironically, it was a Republican further to the right, a member of the Tea Party, that dealt a serious blow this year to the senator. In a brutal party primary in August, physician Milton Wolf accused the mild-mannered Mr. Roberts of losing touch with the voters, largely as a result of almost never being in Kansas. The charge stuck.

Mr. Roberts survived that GOP internal ballot but, with 48 per cent, garnered less than half of the votes cast. Dr. Wolf captured 41 per cent and fringe candidates took the rest. The results left Kansas Republicans divided going into November's election, and many moderate Republicans tell pollsters they are opting for Mr. Orman.

A group of former legislators known as Traditional Republicans for Common Sense has endorsed the independent, as has a bipartisan women's organization. Both say they like Mr. Orman's emphasis on being a pragmatic problem-solver not hung up on party gamesmanship.

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Former Republican senator Nancy Kassebaum, a daughter of the late governor, Alf Landon, and a leading moderate, pointedly refused to record an advertisement endorsing the Republican.

Until now, Sen. Roberts himself has been the issue of the campaign. Even his claim to legislative fame – the 1996 Freedom to Farm Act that deregulated agriculture – put more money into the pockets of Big Agriculture than of the farmers who might otherwise cast ballots for him.

In surveys of how the candidates are perceived, Sen. Roberts is viewed negatively by 47 per cent of the people polled, and positively by 39 per cent (the difference gives him a net rating of –8). Mr. Orman, who has never held elected office, is viewed positively by 39 per cent and negatively by 24 per cent (a net rating of +15).

Facing this dismal situation, the national Republican Party took command of the Roberts campaign last month, dismissed his long-time laid-back campaign manager and brought in professionals from Washington. They put the senator, along with Tea Party favourite Ted Cruz from Texas, on a bus last week making a whistle-stop tour of the state and flooded the media with ads, most of them attacking Mr. Orman.

The commercials, on TV and online, are paid for by organizations such as Americans for Prosperity and Freedom Partners Action Fund, both fronts for money from conservatives Charles and David Koch, owners of Koch Industries of Wichita, the second richest private company in the United States.

The spots portray Mr. Orman as being in league with the reviled liberal Barack Obama. Mr. Orman acknowledges that he voted for Mr. Obama in 2008 and contributed to both his and Hillary Clinton's primary campaigns for the Democratic nomination that year. But he voted for Republican Mitt Romney in 2012, he says. Pro-business Republicans even are trying to use Mr. Orman's financial success against him.

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"The Roberts campaign is desperate," said Patrick Miller, a political scientist at the University of Kansas in Lawrence. "They have no choice but to go scorched earth," he said. "They need to make Orman the issue."

For conservative Republicans, Mr. Orman's stand on a number of policies is the issue. He is conservative on most economic issues but favours choice when it comes to abortion, gay marriage, a path to citizenship for undocumented immigrants (with beefed-up security at the southern border to keep more out), and background checks of people buying guns at gun shows. He thinks the Obama health-care program should be fixed, not repealed, and that evolution should be taught in schools.

"People are fed up," says Tim Orman, the candidate's father, owner of a furniture store and a life-long Republican. Those TV ads attacking his son are "exactly what's wrong with Washington today."

"People here remember an era of moderation and common sense, not ideology," the elder Mr. Orman added.

His son ran briefly as a Democrat for Senate a few years ago. "He dropped out after six weeks," his father said. "And he personally paid back every donation" that had been made to his campaign, a total of $600,000, he said.

"A lot of things have gone right for Orman in this campaign," said Prof. Miller, allowing him to gather Democrats, moderate Republicans and independents.

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Traditionally, "independents are less educated voters," he noted – the people who don't vote. "The more educated the person the more committed to a party he or she tends to be."

Mr. Orman does appear to have tapped into something new: the intelligent independents, like him. And such people may not be limited to this state.

In South Dakota, former GOP senator Larry Pressler is running as an independent and giving the incumbent Republican a run for his money, all on a campaign that sounds a lot like Mr. Orman's.

A decade ago political analyst Thomas Frank published a book called What's the Matter With Kansas? He noted that things that begin here – the Civil War, Prohibition, prairie populism, desegregation – tend to go national.