Pat Roberts survived the toughest challenge of his political career Tuesday, as Kansas voters returned him to Washington for a fourth — and likely final — term in the U.S. Senate.

Roberts defeated a stiff challenge from independent Greg Orman, an Olathe businessman who mounted an improbable insurgent campaign that upended conventional wisdom and the state’s GOP hierarchy.

With 93 percent of precincts reporting, Roberts had roughly 53 percent of the vote to 43 percent for Orman.

At a victory celebration in Topeka, the 78-year-old senator was ecstatic.

“Thank you Kansas!” he said. “Tonight, Kansas stood up and said, ‘Enough.’ Enough of the gridlock. Enough of the failed leadership.”

Orman gathered with supporters in Overland Park. He conceded the race, but insisted that Kansas voters had sent Washington a message — that members of Congress can’t hide behind party labels.

“You have to go there and get stuff done,” Orman said. “That’s the message you helped me send today.”

The state’s decision to send Roberts back to the Senate would not have been a surprise a year ago. Roberts has long been the best-known Republican in a Republican state. Most assumed he would cruise to victory in 2014.

But as the year began the political landscape began to rumble under Roberts’ feet.

First, tea party challenger Milton Wolf rocked the Roberts campaign, calling the longtime politician out of touch. A February story in The New York Times suggested Roberts’ real residence was in Virginia, further damaging the incumbent’s reputation.

Roberts mounted a shaky response, declining to debate Wolf and struggling to explain his choice of residence. He failed to get half of his party’s vote in the August primary against Wolf.

After that close call, Roberts professed confidence in his chances in the November election. Polls showed the Republican defeating Orman and Democratic opponent Chad Taylor in a three-way race.

But Roberts’ weakness immediately provoked whispers that Taylor would abandon the race, leaving Roberts and Orman in a one-on-one match-up. Taylor strongly denied the rumors — then electrified the state by dropping out in early September.

The decision touched off a legal battle that reached the state Supreme Court. Republicans found themselves in the awkward position of arguing the Democrat should stay on the ballot, while Democrats wanted Taylor off — believing their candidate would struggle in a three-way match with the Republican senator and a well-funded independent.

Eventually, Taylor was allowed to withdraw.

Orman quickly surged in the polls. Republicans — initially believing Roberts was safe in a heavily Republican state — were forced to spend more than $10 million to try and defend the incumbent.

All spending in the race may top $30 million, by far the most ever in a Kansas campaign.

Roberts’ poor showing in his primary race prompted a shake-up in his campaign team. Longtime aide Leroy Towns was replaced as chief strategist by a veteran team of GOP operatives schooled in tough, aggressive campaigns.

They launched several bitter attacks against the independent Orman. They accused the businessman of shady connections and argued he was a “liberal Democrat” who supported President Barack Obama.

The ads and postcards had the desired effect. They reduced Orman’s lead and made the race, polls suggested, a dead heat in its final weeks.

Roberts relied heavily on surrogate campaigners and endorsements in the closing weeks of the race. GOP stalwarts Mitt Romney, Bob Dole, Sarah Palin and Sens. John McCain and Rand Paul campaigned for the incumbent, and a reliable GOP turn-out-the-vote operation cranked into gear.

But Tuesday night, Roberts said he was always sure of victory.

“This was not a near-death experience,” he told The Star. “I always had confidence we would win. I just thought we were right.”

Republicans were not surprised by Roberts’ victory, but they didn’t expect such a healthy margin. Ten days before the election, they believed the race was essentially tied. After the results, they believed last-minute ads and campaign appearances swung undecided voters to their side.

Orman did not ask for outside help. Instead, his campaign — financed in large part by the candidate himself — relied on an early barrage of TV commercials portraying the candidate as a true independent.

One ad showed a blue-versus-red tug of war, illustrating Orman’s argument against the two major parties.

Orman called himself “socially tolerant and fiscally moderate” during the campaign. He supported same-sex marriage and access to abortion, traditionally Democratic party positions, and said it would not be possible to repeal the Affordable Care Act.

He did criticize some federal regulations, and supported some tax reform proposals, both closer to Republican party positions.

Roberts’ own efforts tacked significantly to the right this election year. He opposed a federal spending bill that included significant spending in the state and voted against the farm bill. He also opposed a disability treaty supported by former Sen. Dole.

Orman had outside help. A group called the Committee to Elect an Independent Senate spent more than $3 million for ads supporting the challenger. Mayday PAC spent more than $900,000 on Orman’s behalf.

At the same time, Orman declined to accept direct contributions from political action committees. PACs gave Roberts more than $2.7 million.

In the end that spending, and Roberts’ deep familiarity with voters, proved enough to get him over the top. His re-election is a deep relief to the national Republican party, which now controls the Senate and the U.S. House.

“Now it is time for action,” Roberts said Tuesday. “And this Marine is ready to lead that charge.”