"We have a Mourdock versus Mourdock debate going on. They're not my words, they're your words," Donnelly said.
Donnelly and Mourdock spent about as much time looking at each other as they did the camera, trading the same accusations they've made throughout their tight Indiana Senate battle. Mourdock repeatedly tied Donnelly to President Barack Obama and his policies and challenged him to explain his views. For his part, Donnelly continued to hit Mourdock for comments that he would seek less bipartisanship if elected.
"I think we need to be saying here principle is more important than partisanship. We can't just have people caving in because of partisanship," Mourdock replied, repeating an argument that bipartisanship in Washington used to mean Republicans bowing to Democratic requests for more spending.
Libertarian Andrew Horning joined the two on stage, often outside the battle. He argued Donnelly and Mourdock are no better than "cogs in the machine" that had left the nation with massive debt.
The three men squared off in the first of two debates Monday night at the WFYI studios in Indianapolis. It was the same location Mourdock and U.S. Sen. Richard Lugar met in April. A few weeks after that meeting, Mourdock beat Lugar by a 20-point margin in the Republican primary.
Indiana's battle is among about a half dozen races that will determine which party controls the Senate and has drawn national attention and money from outside groups.
Since the primary, Mourdock has struggled to bring moderate "Lugar Republicans" back into the fold, with polling consistently showing Republican presidential candidate Mitt Romney and Republican gubernatorial candidate Mike Pence outperforming Mourdock by a dozen or so points.
The challenge for Mourdock has been to refocus the race away from him and onto Donnelly. Mourdock's early stumbles — from his comments about compromise to fundraising appeals that continued to hit Lugar well after the primary was over — placed him on the defense and spurred Republican senators to flock to the state in an attempt to bolster his credibility.
Donnelly has run a steady campaign but was forced to defend unpopular votes such as his support of the federal health care law and his 2008 endorsement of Obama.
The race has been dominated by outside spending from Republican- and Democrat-aligned groups, including the conservative Crossroads GPS and Senate Majority Leader Harry Reid's super PAC.