Indiana Senator Richard Lugar and state Treasurer Richard Mourdock meet Wednesday night in Indianapolis for what's expected to be the only debate of their primary battle.

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Polls indicate a quarter of Republican voters are undecided, but IUPUI political analyst Brian Vargus is skeptical the debate will make up their minds. He says it would take either a gaffe or a clear-cut winner -- and even then, he says the undecided voters are less likely to be paying close attention.

Vargus says Mourdock needs to drive home his argument that Lugar's record is at odds with what conservative voters believe, without duplicating the ads' bare-knuckled tone. He says Lugar needs to keep the focus on his recent votes -- not only because they're more consistently in tune with the conservative base, but because he needs to keep voters from thinking about how long he's been in Washington.

Vargus says Lugar may benefit from Rick Santorum's decision to end his presidential campaign. He says Mourdock and Santorum share a base among conservative evangelicals, ordinarily a high-turnout demographic. But Vargus says Santorum's withdrawal may dampen enthusiasm, while Lugar will benefit from unusually strong support from the G-O-P establishment, from Governor Daniels on down.

The debate will air live on wibc.com beginning at 7 p-m, and on 93 WIBC at approximately 10:30, following the conclusion of the Pacers-Cavaliers game.