Republicans in Washington say they tried to warn Richard Lugar that this could happen.
With his seventh Senate term on the line Tuesday in Indiana's primary, Lugar is now 10 points down against his Republican challenger, Richard Mourdock, the two-term state treasurer who has run an aggressive campaign painting Lugar as an out-of-touch Washingtonian, a man known nationally as a statesman who is too liberal for the state's conservative voters.
"Lugar's team was warned in the beginning of 2011," says a top Republican aide familiar with the conservations between Lugar's side and national GOP leaders, who huddled after a series of incumbent Republicans went down in defeat in the 2010 primaries. "We walked through everything that Bob Bennett, Lisa Murkowski, and Mike Castle had done wrong in not taking their primaries seriously enough. Those lessons were not heeded."
Instead, the aide said, Lugar went into 2011 as he had all six previous election cycles, when the senator never drew a primary opponent and had just one serious Democratic challenge over the course of his 36-year Senate career.
But the 2012 cycle has proved different for Lugar in every way, with a well-funded challenger, outside conservative interest groups spending millions to unseat him, and, most important, a series of embarrassing episodes prompting questions of whether he could even vote in the state at all. These questions reinforced growing complaints from local Republicans that they rarely, if ever, saw Lugar at local GOP events, or even working the state, throughout his career.
Although Lugar owns a family farm in Indiana where his son lives, he sold his primary residence, a house in Indianapolis, in 1977 after winning his Senate seat. In March, Lugar circumvented a ruling that he and his wife could not vote in Indiana because he does not legally live there, by re-registering though the farm's address.
Later that month, Lugar admitted that he did not know which address is printed on his Indiana driver's license, but said he believed it was the address of the house he sold in 1977.
The controversies seemed small compared with Lugar's legacy of being a leading national voice on foreign affairs, including his sponsorship of a bill to disarm the former Soviet Union's nuclear arsenal. But they also opened the door for Mourdock to convince Hoosier Republicans that Lugar had literally gone Washington in a year when Washington has never been less popular. In their only debate, he took aim squarely at Lugar.
"The first thing I'm going to do to represent Hoosiers is to be in touch with them," Mourdock said. "I'm proud to call this state home ... It is a place that if I have the privilege of serving as your U.S. senator, I'm not moving from. I will always call Darmstadt, Indiana, home."
Mourdock also has accused Lugar of being insufficiently conservative, pointing to the incumbent's votes on TARP and the auto bailout, as well as votes to approve Sonia Sotomayor and Elena Kagan to the Supreme Court.
But issues alone are rarely enough to turn an incumbent out of office, and Mourdock has been aided immeasurably by outside conservative groups, including the Club for Growth, Red State, and Freedom Works, along with high-profile endorsements from Sarah Palin and Michele Bachmann, which have all combined to make him a well-funded, well- known challenger fully capable of knocking off a weakened incumbent.
Democrats are rooting for a Lugar loss, saying that a Mourdock win would make the seat a prime pickup opportunity in November. But they see Mourdock more as a Ken Buck, who posed a serious but losing challenge to Colorado incumbent Sen. Michael Bennet, and less of a Christine O'Donnell, whose victory in the Delaware Republican primary all but handed the seat to Democrats in 2010.
"If Mourdock is the nominee, that poses an even greater opportunity for us," says Matt Canter, communications director for the Democratic Senatorial Campaign Committee. "He is 2012's Ken Buck. He has the same views and he expresses them in the same aggressive, offensive, polarizing way that turns off independents and swing voters. We're very bullish that we have the right candidate to compete in Indiana this fall."
But Republicans, privately and publicly, say they believe that either Lugar or Mourdock can hold the seat.
"No matter who emerges from Tuesday's primary, there's no question that Republicans will hold this seat in November," says Brian Walsh, communications director of the National Republican Senatorial Committee. "Frankly, I'd be surprised if national Democrats even invest in the state."
Whichever Republican wins the primary will face Rep. Joe Donnelly, a lawyer and businessman who won a Democratic House seat in 2006 in a mostly Republican district, and held onto his seat in the 2010 elections that saw 87 new Republicans swept into the chamber.
Democrats' internal polling from late March showed Donnelly beating Mourdock by six points, a margin they believe can increase with a heavy appeal toward independents who might have favored Lugar instead.
"Independents are going to decide this election. They are going to be looking for a home and Joe Donnelly is going to be well-positioned to appeal to those voters," says Canter. "Richard Mourdock is not."
Democrats have been quick to identify Mourdock as a Tea Party Republican, while the GOP has downplayed such ties, saying Mourdock is a statewide Republican who will be happy to take any support, including from the Tea Party.
But Jacqueline Bodnar, press secretary for Freedom Works, explains that Mourdock first came to the attention of Tea Party activists when he rode a bus from Indiana to Washington with Tea Party supporters to their first "9/12 Rally" in front of the Capitol, where Mourdock was a featured speaker. Many of those activists formed Hoosiers for a Conservative Senate and are the foundation of his grassroots support.
Bodnar says that because Mourdock has pledged to vote to repeal the Obama health-care law, pass the "Cut, Cap, and Balance plan" to balance the budget, and has said the Paul Ryan budget needs more cuts, she doesn't particularly care what label Mourdock uses in the campaign.
"At the end of the day what he classifies himself as doesn't really bother me, because we know that he's going to make the right vote," she says. "As long as he identifies as a constitutional conservative, I'm good with that."