(CNN) – One of the nation's most bitterly fought U.S. Senate races – the battle in Ohio between incumbent Democratic Sen. Sherrod Brown and Republican state treasurer Josh Mandel - devolved into the GOP candidate calling his rival a liar at a debate Thursday.
Mandel was responding to charges from Brown that he skipped meetings as treasurer, and was attempting to skip rungs on the political ladder.
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"Senator, you are a liar," Mandel told Brown. "You are lying to the people of the state of Ohio. You are falsely attacking me, and I won't stand for it. You might want to try to push people around in Washington, but you're not going to push me around."
That charge drew an incredulous response from Brown, a first term Democrat.
"It's just a pretty remarkable thing for a young man to say, or a man of any age to say, in a debate," the senator said, drawing attention to Mandel's relative youth. The GOP candidate is 35.
"Senator, the reason you're agitated and frustrated tonight is because the people of Ohio disagree with you," Mandel charged.
Brown responded, "I don't need a lecture from somebody who can't wait to get to the next job and run for higher office and continue to try and move up the ladder."
Over $21 million has been spent on the Buckeye State race for the U.S. Senate, according to Federal Election Commission data. Both the Rothenberg and Cook political reports rate the Senate race as leaning in Brown's favor.
On Friday the conservative group Club for Growth said it was spending $800,000 to air a television ad around Columbus calling Brown "foolish on taxes."
An NBC/Wall Street Journal/Marist poll taken October 7-9 showed Brown leading Mandel, 52%-41%.
Ohio is also a key battleground in the presidential race.