Sen. Richard Lugar (R-Ind.) lost his primary on Tuesday, becoming the latest Republican to fall victim to a tea party-fueled opponent.

Results early Tuesday night showed state Treasurer Richard Mourdock leading the six-term senator 61 percent to 39 percent with 40 percent of precincts reporting. The Associated Press has called the race for Mourdock.

View Photo Gallery: Few incumbent senators have lost bids for their parties’ nomination over the last 60 years, making Sen. Richard Lugar’s (R-Ind.) loss on Tuesday all the more newsworthy. We look at Lugar and nine senators whose losses surprised us the most.

Mourdock now becomes the GOP standard-bearer in a state where Republicans have a built-in advantage. But his nomination also opens the door a crack to Rep. Joe Donnelly, a Democrat whose chances improve now that he doesn’t have to face the more moderate longtime incumbent.

Lugar is the third GOP senator to lose a primary since 2010, joining Sens. Lisa Murkowski (R-Alaska) and former senator Robert Bennett (R-Utah). Also in 2010, tea party candidates upended establishment favorites in Senate races in Colorado, Delaware and Nevada, and went on to lose all three races in the general election. Unlike previous tea party usurpers, though, Mourdock is a statewide elected official.

Then-Sen. Arlen Specter (D-Pa.) also lost a primary in 2010 after switching parties.

After his loss, Lugar said he would support Mourdock but also said his opponent needs to adjust his political approach.

“His embrace of an unrelenting partisan mindset is irreconcilable with my philosophy of governance,” Lugar said in the statement, according to reporters present. “His embrace of an unrelenting partisan mindset is irreconcilable with my philosophy of governance.”

Lugar is likely to be the only incumbent senator to lose re-nomination this year. Sen. Orrin Hatch (R-Utah), who along with Lugar is tied for the longest-serving Republican in the Senate, avoided a top-tier challenge and appears to be on a path for victory in his primary next month.

Mourdock lost five campaigns before being elected state treasurer in 2006. He was reelected in 2010 with 62 percent of the vote, and soon after launched his Senate campaign.

He earned the backing of several conservative groups, most notably the National Rifle Association and the fiscally conservative Club for Growth, which spent nearly $2 million to defeat Lugar and helped Mourdock close the gap financially.

“Richard Mourdock’s victory truly sends a message to the liberals in the Republican Party: voters are rejecting the policies that led to record debt and diminished economic freedom, and they will continue to be rejected in elections throughout America,” said Chris Chocola, a former Indiana congressman who is now president of the Club for Growth.

President Obama won Indiana in 2010 but isn’t expected to seriously compete for the state this year, as the state has returned to its more conservative roots.

Donnelly was one of few Democrats to survive in a tough district in 2010, and Democrats hope he can bring broad appeal to the Senate race. But so far, he has struggled to raised money for his campaign.

Democrats immediately set about comparing Mourdock to previous tea party candidates, including 2010 Colorado GOP candidate Ken Buck.

“Richard Mourdock is this year’s Ken Buck,” said Guy Cecil, the executive director of the Democratic Senatorial Campaign Committee. “Tonight’s results make the Indiana Senate race a toss-up race.”

Republicans immediately set about tying Donnelly to Obama.

“Hoosier voters are ready to put an end to Joe Donnelly and President Obama’s liberal agenda of higher taxes, bigger government and reckless deficit spending,” said Sen. John Cornyn (R-Texas), the chairman of the National Republican Senatorial Committee. “That is why I am confident they will elect a proven statewide leader like Richard Mourdock who will fight every single day on behalf of Hoosier values, and not the Obama agenda.”

Obama, whose friendship with Lugar was regularly used against the senator, expressed regret that his “friend” had lost.

“As a friend and former colleague, I want to express my deep appreciation for Dick Lugar’s distinguished service in the United States Senate,” Obama said in a statement. “While Dick and I didn’t always agree on everything, I found during my time in the Senate that he was often willing to reach across the aisle and get things done.”

Other Democrats were equally as kind, with Sen. John Kerry (D-Mass.) going so far as to label Lugar’s loss “a tragedy for the Senate.”

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