Republican Richard Mourdock and Democrat Joe Donnelly dove into their first televised debate Monday by framing the race for the U.S. Senate as a high-stakes battle between upholding partisan principles and reaching across party lines.

Mourdock, a Tea Party favorite who knocked off longtime U.S. Sen. Richard Lugar in a brutal May primary, drew himself as the “principled” man who would withstand the temptation to compromise, and blamed the unwillingness of others to do so for the country’s $16 trillion national debt.

Democrat Joe Donnelly hailed the virtues of bipartisan collaboration, blamed Mourdock’s “principles” for nearly destroying the auto industry in Indiana, and called Lugar — the man Mourdock forced into retirement — a “true American hero” that more politicians should emulate.

The third party candidate, Libertarian Andy Horning, used the sharp exchanges between the men to argue that disenchanted voters should pick him.

“I think you’re going to see what’s going to happen,” Horning said, after Donnelly and Mourdock threw some verbal elbows at each other. “It’s always going to be a tug of war and you’re always going to lose.”

Mourdock and Donnelly warred with each other through the debate, hitting on points highlighted in their escalating series of TV ads that paint their opponent as a force for no-good. Mourdock blamed Donnelly, a U.S. Congressman from South Bend, for helping to blow up the federal budget.

“I think that principle is what is really at stake here, and I stand with the principle that government has grown too big and costs too much,” Mourdock said, early in the debate.

Donnelly seized on the comment to draw attention to Mourdock’s support from Tea Party members, credited for his toppling of Lugar.

“Your principle is an unapologetic leader of the Tea Party movement, and that’s fine,” Donnelly said. “I would rather make sure that we can work together in Washington and in Indiana to move our country forward.”

Mourdock blamed Donnelly for siding with Obama on a range of issues, including the federal healthcare program known as Obamacare. Donnelly, meanwhile, seized on Mourdock’s 2009 decision, made as Indiana State Treasurer, to try to block the Obama administration’s efforts to restructure Chrysler through tightly-controlled bankruptcy proceedings.

Mourdock called his decision to hire a law firm sue to oppose the Chrysler restructuring as “principled,” saying he did so to protect the state’s police and teacher pension funds, which had invested in Chrysler.

“I think we need to be saying here principle is more important than partisanship,” he said. “We can’t just have people caving in because of partisanship.”

Donnelly countered with, “You, Mr. Mourdock, singlehandedly could have sunk Indiana’s economy and put us into a recession, if you were fortunate enough — fortunate enough for you, unfortunate for us — if you had been successful in your lawsuit in regards to Chrysler.”

Horning frequently jumped into the fray, arguing that Donnelly and Mourdock were no better than “cogs in the machine” that had left the nation with massive debt.

The race for Lugar’s seat in the Senate has captured national attention and brought in millions of dollars from outside groups. Recent polls show Donnelly and Lugar running almost neck-and-neck. Much is at stake: Indiana has become a major battleground in the race for control of the U.S. Senate. Republicans need to gain four seats to take control of the Senate.

Mourdock, Donnelly, and Horning will meet again in their second and final Senate debate on Oct. 23 in New Albany.