An internal poll shows incumbent Democratic Senator Mary Landrieu (D-LA) trails her Republican challenger Rep. Bill Cassidy (R-LA) ahead of December’s runoff by 16 points. This confirms what demographer Elliot Stonecipher has known for some time: the demographics of Louisiana strongly favor Cassidy over Landrieu in next month’s election.

Appearing on The Jim Engster Show Wednesday, Stonecipher said, “Mary Landrieu cannot win the race. Bill Cassidy has to lose it.” 

Earlier on Engster’s show, Louisiana political expert Jeremy Alford said, “the key figure is 18%, which Landrieu polled with white voters.” 

Another Republican who will not be in December’s runoff election, Col. Rob Maness, took in 14% of the vote. Just a day after the jungle primary, Maness endorsed Cassidy. The bulk of his support seems likely to go to Cassidy in the runoff.

That simple math–Cassidy’s 41% combined with Maness’s 14% totals 55%, or 13% more than Landrieu’s 42% in the “jungle primary”–is re-enforced in the internal poll that was released on Thursday.

With Republicans now holding 53 seats in the new Senate, Louisiana’s runoff election, the only Senate race yet to be decided, is not particularly important to Democrats nationally. They have virtually ended their support for Landrieu’s television advertising. 

Earlier on Engster’s show, Alford noted: “in the runoff, Bill Cassidy and the Republicans have accounted for 96% of the television ads so far. I don’t think we’ve ever seen Mary Landrieu in a position like that before.”  

But Alford sounded a note of caution. “If anyone can pull this off,” he observed,”it’s Mary Landrieu.” Despite unfavorable polls and a national wave of opposition to President Obama’s policies, Landrieu is campaigning vigorously across the state. 

Cassidy and Landrieu have agreed to meet in one debate prior to the runoff election. Landrieu, running from behind, wants more debates, but Cassidy has responded to that desire cleverly, according to Alford.

“He’s said he’ll agree to one additional debate with Landrieu for every day President Obama comes to Louisiana to campaign on her behalf,” Alford said.

No one in Louisiana expects Landrieu to take Cassidy up on that offer.