Rep. Bill Cassidy (R-La.) said a new campaign ad from Sen. Mary LandrieuMary LandrieuCNN producer on new O'Keefe video: Voters are 'stupid,' Trump is 'crazy' CNN's Van Jones: O'Keefe Russia 'nothingburger' video 'a hoax' Trump posts O'Keefe videos on Instagram MORE (D-La.) that shows him stumbling over a speech and calls him “nearly incoherent” was released out of “bitter desperation” on the part of the Democratic senator.

“They took a two-second clip out of a 15-minute speech. If you look at the whole 15-minute speech, I think I did a pretty good job,” Cassidy told Fox News’s Megyn Kelly on Tuesday night. “This kind of shows a bitter desperation, I think. She knows she’s on the wrong side of the issues, so instead of talking about the issues, she makes up things about the [Veterans Affairs] hospital or she attacks me personally.”

The Landrieu campaign ad, released over the weekend, ran during the New Orleans Saints game. It shows Cassidy giving a speech at the Republican Leadership Conference earlier this year, and highlights various moments from the speech where he appears to trip over his words.

The ad describes the Republican lawmaker as being “nearly incoherent” before the narrator asks: “We’d lose Mary Landrieu’s clout for this?”

“I may not speak like Barack Obama, she prefers Barack Obama, but I tell you — I speak on the right side of the issues for the people of Louisiana, and that’s why I’m going to win on Dec. 6,” Cassidy said Tuesday.

A runoff election between Landrieu and Cassidy is set for Dec. 6. Cassidy leads by nearly 5 percentage points, according to the RealClearPolitics average of polls.