A new radio spot supporting Sen. Mary LandrieuMary Loretta LandrieuCassidy wins reelection in Louisiana Bottom line A decade of making a difference: Senate Caucus on Foster Youth MORE (D-La.) says that Republicans will impeach President Barack ObamaBarack Hussein ObamaBiden teams to meet with Trump administration agencies Biden says he'd meet with Trump 'if he asked' Biden-Harris ticket the first in US history to surpass 80 million votes MORE if her runoff opponent, Rep. Bill Cassidy (D-La.), wins.

“They have shown our president so much disrespect,” says Rep. Cedric Richmond (D-La.) in the ad, which was first reported by BuzzFeed News.

“They said he wasn’t a U.S. citizen, they even sued him — and if Cassidy wins, they will impeach him.”

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The ad ends with the message that it is "[a]uthorized by Friends of Mary Landrieu, and paid for by the Democratic State Central Committee of Louisiana.” Landrieu lends her approval at the beginning of the ad.

It’s the latest salvo in the runoff, which will decide Landrieu’s political future.

With the race in its final stretch, Landrieu’s campaign has sought to capitalize on new information that indicates Cassidy might have improperly billed the state’s flagship university.

Last month, she mounted a last-ditch effort to pass a bill approving the controversial Keystone XL pipeline, but came up one vote short.

Landrieu, who chairs the Senate’s Committee on Energy and Natural Resources, has argued that her clout on energy policy makes her an asset to Louisiana. Republicans have pledged to give Cassidy a seat on the committee, when they take over the majority in January.

The longtime senator is fighting an uphill battle. Polls before Election Day indicated that once a Tea Party candidate was eliminated, Cassidy would have an edge with voters.

The runoff will be held on Dec. 6.