(CNN) – It's been 12 years since Indiana Sen. Dick Lugar faced off in a campaign debate.
That streak ends Wednesday night when the most senior Republican member of the Senate shares the stage with his conservative GOP challenger, Indiana State Treasurer Richard Mourdock, at a debate in Indianapolis that will be televised statewide in Indiana.
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The six-term senator has not faced a primary challenge since first winning election to the Senate in 1976, and six years ago he ran un-opposed for re-election. The last time he debated was in his 2000 re-election.
But this time around Lugar faces a serious challenge from Mourdock, who has strong backing from local and national tea party groups as well as from such major organizations as the powerful National Rifle Association and the fiscal conservative Club for Growth. Both groups went up with campaign commercials this week supporting Mourdock.
Lugar's been criticized by many tea party activists and other grass-roots conservatives for his willingness in the past to work with Senate Democrats to seek bipartisan solutions, for his votes in favor of President Obama's Supreme Court nominees, and for his 2008 vote in favor of the Troubled Asset Relief Program, better known as TARP. They are also upset with Lugar, the ranking Republican on the Senate Armed Services Committee, for his early public openness to vote in favor of the New Strategic Arms Reduction Treaty (New START) with Russia.
Lugar, the former mayor of Indianapolis who turned 80 last week, did oppose President Obama's health care reform measure, voting against the Affordable Health Care Act. And like most Republicans, he's a supporter of the controversial Keystone pipeline project.
Lugar's opponents, as well as state and national Democrats, are trying to portray the longtime senator as a Washington insider. Lugar's residency in Indiana has been repeatedly questioned in the past, but the senator beat back a challenge in February when the Indiana Election Commission determined he wasn't required to be a resident of Indiana to appear on the ballot – as he had been serving the state as senator while living away from the state. Lugar has lived in McLean, Virginia since the sale of his Indianapolis home in 1977.
And last month, an election commission in Indianapolis ruled Lugar was ineligible to vote in his former precinct because he no longer resided at the address on his voter registration.
Lugar's trying to turn the argument back on Mourdock. In a campaign commercial running statewide this week, Mourdock's accused of selling out to "DC outsiders."
Wednesday night's debate is the only one before the May 8 primary. If Lugar may be rusty when it comes to debates, Mourdock is even more out of practice. He didn't debate in his 2006 election to state treasurer or his re-election in 2010. The last time he's faced off in a debate was his unsuccessful 1992 bid for Congress.
A poll released last week indicated Lugar with a single digit lead over Mourdock. Democrats see an opening, hoping that a Mourdock victory will make the race more competitive in November. The winner of the GOP primary will face off against Democratic Rep. Joe Donnelly in the general election.
Democrats currently have a 53 to 47 advantage in the Senate, including two independents who caucus with the party. But the Democrats are defending 23 of the 33 seats in the chamber that are up for grabs this November.
CNN's Kevin Liptak contributed to this report