Indiana voters head to the polls Tuesday for the state’s primary election, and all eyes are on the Republican race for U.S. Senate.

Six-term incumbent Richard Lugar is trying to survive a strong test from the right. Lugar is 80 years old and has spent 35 of them in the Senate, a length of service that’s been a liability this year.

“When Dick Lugar moved to Washington in 1977, disco topped the charts and leisure suits were in style,” begins a TV ad from Lugar’s opponent, state Treasurer Richard Mourdock.

Mourdock’s labeled Lugar out of touch with Hoosiers and too close to the president.

“No wonder they call him Obama’s favorite Republican,” a narrator says in another ad, using a common tagline of the Mourdock campaign.

For his part, Lugar’s attacked those attacks.

“Richard Mourdock and his DC cronies offer nothing but the politics of personal destruction,” states a Lugar television ad.

And Lugar’s leaned on popular Gov. Mitch Daniels to talk up the senator’s conservative creds.

“We’re lucky to have Dick Lugar and we need to keep him,” Daniels, dressed casually while strolling in the countryside, says to the camera.

Those ads were paid for by the campaigns themselves, but this race has also been a target of outside money. According to the Center for Responsive Politics, the total tops $4 million in non-candidate spending, the most out of any race in 2012 besides the presidency.

The conservative group Club for Growth has gone on a Hoosier spending spree, attacking Lugar.

“What’s happened to Dick Lugar? He was a respected national leader, a statesman,” the ad says. “Then he became part of the problem.”

Lugar’s also been helped by outside money, including from a group that calls itself Hoosiers for Economic Growth and Jobs.

“Who put the for sale sign up on Indiana?” one man asks another in an ad from the group.

“Indiana’s not for sale,” laughs the other man.

“Richard Mourdock thinks so,” the first man replies. “Some DC special interest group, Club for Growth, is trying to buy our Senate seat.”

Another group supporting Lugar, called American Action Network, spent more than $600,000 in the race. But in a sign of Lugar’s slip in the polls, the group recently halted its ads.

“We’ve decided we’re going to let this race play out,” said Dan Conston, a spokesperson for AAN.

The winner of the Republican Senate primary will face the only Democrat on the ballot, U.S. Rep. Joe Donnelly, in the fall.