Hard to say how credible this poll is, but all political observers following the Louisiana Senate runoff scheduled for December 6 agree that Republican Bill Cassidy has opened a significant lead over incumbent Democratic Senator Mary Landrieu.

One aspect in favor of this poll's accuracy is that Landrieu recieved 42% of the vote on election day and shows her support at 40% in this new poll. And if you combine Cassidy's 40% on election day with the other conservative Republican candidate Maness's 14%, the total is well within the margin of error of the new poll

The Hill:

Rep. Bill Cassidy (R-La.) has opened up a 16 point lead over Sen. Mary Landrieu (D-La.) in their Louisiana Senate runoff, according to an internal poll conducted on behalf of the Cassidy campaign and obtained by The Hill. 

Cassidy takes 56.6 percent against Landrieu’s 40.5 percent in the poll conducted by Magellan Strategies. While internal polls should be viewed with some skepticism, it’s the first head-to-head poll to be released in the runoff period. The RealClearPolitics average of polls taken before Election Day showed Cassidy up by only 5 percent in the head-to-head matchup.

A source close to the Landrieu campaign strongly pushed back against the poll, arguing that it’s an automated, push-button poll conducted by a conservative outlet, it used loaded terms to survey only issues pertinent to the Cassidy campaign, and that it underestimates Landrieu’s popularity among African American voters.

On Election Day, Landrieu took 43 percent in a field where Republicans split the vote. Cassidy trailed in at 42 percent, and Tea Party candidate Rob Maness at 14 percent. Louisiana’s election rules require a run-off on December 6 between the top two candidates since no candidate topped 50 percent of the vote.

Maness has since rallied conservatives to back Cassidy. Influential conservatives like Sen. Rand Paul (R-Ky.), Gov. Bobby Jindal (R-La.) and Sarah Palin have endorsed Cassidy and are participating in “unity rallies” to help him unseat Landrieu.

Louisiana Democrats say that Republicans are late to rally behind Cassidy because he doesn’t inspire confidence within GOP circles. They also point to Maness’s double-digit support in the general election and say those Louisiana voters won’t turn out for Cassidy in the runoff just because national Republicans have now taken an interest in the race.

According to the poll, Landrieu’s big lead among African-American voters – she takes almost 90 percent in the poll to Cassidy’s 7 percent – isn’t enough to make up for Cassidy’s strength among white voters, who in exit polls made up about 75 percent of the electorate in 2014.

All will depend on turnout, of course, and with Maness fully on board and the national GOP involved, Cassidy's get out the vote operation should be good enough to carry him to victory.