Democratic Senator Mary Landrieu is trailing her Republican challenger by a giant 16-point margin in a runoff for one of Louisiana's two U.S. Senate seats, according to poll results obtained by MailOnline.

The survey, commissioned by GOP Rep. Bill Cassidy's campaign, was leaked to media in order to fire a shot over the senator's bow and send a signal to energy lobbyists that her ship is taking on water.

It suggests that Democrats' worst fears have been realized even though Landrieu edged Casssidy by 1 percentage point on Election Day.

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GOP Rep. Bill Cassidy's campaign commissions polls daily, and the latest results show him in a commanding position over Democratic Sen. Mary Landrieu

Cassidy, a medical doctor, finished a close second on Election Day but appears to have a clear advantage going into the Dec. 6 runoff; Incoming Senate Majority Leader Mitch McConnell says if he wins he'll get a seat on the Energy Committee – undercutting Mary Landrieu's strength in an oil-and-gas-heavy state

A second Republican candidate, Rob Maness, won 14 per cent of the vote on Nov. 4, enough to deny them both the 50-percent showing required to avoid a December 6 runoff.

Now Maness has endorsed Cassidy, helping him erase his 1-point deficit with Landrieu and adding far more.

Cassidy is 'trying to shut K Street down for Mary' by selectively releasing the polling data, a source close to his campaign in Louisiana told MailOnline.

'The energy folks, the lobbyists, keep trying to say she has a chance to win. That's why it was leaked.'

Landrieu has lined up for what Republican Capitol Hill aides are calling the 'Hail Mary XL,' a legislative strategy to save her Senate seat by winning a vote to approve the Keystone XL pipeline, which would bring 700,000 barrels of oil daily from the Canadian province of Alberta to the Gulf coast.

She may get her chance on Tuesday if she can find 14 other Democrats in the lame-duck Senate to join her in backing the project's construction. All 45 Republicans have already signed on.

As of Thursday one whip count shared with MailOnline found that she was just two votes short, giving her a 58 of the 60 votes she will need to override Senate Majority Leader Harry Reid's objections and force a roll call.

Republicans have fired back by making Cassidy the public face of the House bill. And Sen. Mitch McConnell, the Kentuckian who will be the Senate's majority leader in January, vowed to give him a seat on the Energy Committee if he wins.

Landrieu's re-election campaign has rested squarely on the question of whether she has enough clout as the committee's current chairwoman to pump new blood into Louisiana's sprawling energy infrastructure – including the 16 oil refineries operating there.

She will lose her chairmanship weeks from now regardless of what happens since Republicans will come back in January with a sizable Senate majority.

The GOP campaign source hinted that if Landrieu were to mount a comeback, it would require super PAC funding from the energy industry's deep pockets.

A 16-point deficit, he said, might be enough to convince them to hang her out to dry.

'And down here,' the source added, 'we have to convince people that it's not in the bag.'

Landrieu now lacks the support of any out-of-state PACs, including the Democratic Senatorial Campaign Committee.

Since the outcome no longer affects which party will control the Senate – the GOP will have either a four- or five-seat edge – the DSCC is saving its money for another day.

Landrieu, the outgoing chair of the Senate Energy Committee, is trying to engineer a last-minute vote on the Keystone XL oil pipeline as a 'Hail Mary' play to save her re-election bid

Landrieu communications director Fabien Levy told MailOnline that the GOP's glasses are rose-colored past the point of credibility.

But he wouldn't share any of the Democrat's own internal poll numbers.

'What our numbers show is that Mary Landrieu is in a good position to win big on Dec. 6, just as she's won all of her other close races,' Levy said in a phone interview.

He took issue with the automated nature of the Magellan Strategies poll, which asked respondents to answer questions by pushing telephone buttons instead of talking with a pollster.

Magellan principal Jon Diez confirmed via email that his firm ran a 'push-button' poll for Cassidy's team.

Diez's resulting memo discloses that 1,917 people provided answers, and assigns a 2.2 per cent margin of error to the result.

Levy said that in the Landrieu campaign, 'we don't do automated' polls – only more traditional surveys.

Diez countered with the email equivalent of a shoulder-shrug.

'As with live surveys, there is no way to guarantee that each respondent is honest in their responses,' he said.

Diez also explained that his sample is balanced for race and other demographic features when phone numbers are culled from public voting records.

'Her campaign is running on fumes,' Diez said in an email of Landrieu's re-election efforts.

'She voted 97% of the time with a president and a party who 62% of the voters [in Louisiana] disapprove of. It is what it is.'

Levy also objected to a series of set-up questions asked immediately before respondents were asked to choose a future senator.

A recorded message asked Louisianans to decide which of four issues should be 'the top priority' for the next Congress. The only issues on the list were repealing Obamacare, protecting the U.S. from terrorists, ramping up border security and 'addressing the illegal immigration problem,' and shrinking the size of government.

Cassidy lost on Election Day but looks to be leading in the runoff since the other Republican in the race is supporting him

Reputation on the line: Former Secretary of State Hillary Clinton posted a disappointing record on Election Day, with losses raining down on six of the nine Senate candidates she stumped for; a Landrieu win could diminish the feeling that her star is on the wane just as the 2016 presidential season gets ready to kick off

Levy called those 'push-poll questions' that might cause Democrats to hang up before the crucial questions were asked.

He also noted that the Keystone XL pipeline didn't make the cut.

'He's pretending it's important now, but where has he been on the pipeline?' he asked.

One of the run-off contest's most comical features has been the tit-for-tat skirmishes over the number of times Landrieu and Cassidy will debate.

'We challenged him to six debates ... one for every year he wants to serve in the Senate,' Levy said of the Landrieu campaign's symbolic challenge. 'He only agreed to one.'

In 2002, the last time Landrieu faced a runoff election, she debated her opponent four times in the weeks following Election Day.

On Tuesday in Shreveport, Cassidy turned the Democrats' challenge on its head.

'She wants to have 6 debates, as if 6 has some significance,' he told KTBS-TV3.

'Why not have 97 debates – one for every percent that she supports Barack Obama? Or 716 for the $716 billion that Obamacare took out of Medicare?'

Bloomberg News reported Wednesday that Cassidy's campaign operation has several advantages in addition to poll numbers.

About 96 per cent of all the TV ads running in all six major media markets there support him.