In back-channel conversations in Washington, the consensus among top Republicans is beginning to form: Vitter has become so damaged by the bitter race --- and the renewed focus on his "D.C. Madam" prostitution scandal -- that he would almost certainly cost his party a valuable Senate seat if he decided to run for a third term.
Republicans hope that the November 21 election will sort itself out and that Vitter will emerge victorious. And the conservative senator does have a strong base of supporters who would embrace him should he lose the governor's race and run for re-election to the Senate.
But with polls showing Vitter growing increasingly unpopular -- and losing by a big margin to his Democratic opponent, state Rep. John Bel Edwards -- a growing number of top Republicans privately say Vitter would need to step aside to help their party maintain control of the Senate.
"It would be best for the party if he didn't run," said one senior Republican senator who, like many others interviewed for this story, asked not to be named with the governor's race still ongoing.
A sample of the nastiness of the campaign: Edwards last week released a jaw-dropping campaign ad
accusing Vitter of soliciting prostitution when he missed a vote in 2001 as a House member to honor soldiers of the first Iraq war.
Senate Majority Leader Mitch McConnell has not yet spoken with Vitter about the matter, two people familiar with the situation said. But senior Republicans are looking at Vitter's poll numbers nervously.
"He's very damaged," said Verne Kennedy, who has done extensive polling on the Louisiana governor's race but is not affiliated with either campaign. "If he can't win the governor's race, it probably damages him to the fact that he can't win reelection to the Senate."
Several polls since last month's primary -- which Edwards won 40% to Vitter's 23% -- show Edwards with a double-digit lead, and Kennedy's surveys found Vitter with 43% of voters viewing him unfavorably. One recent survey, which was conducted for an outside group that has been attacking Vitter, showed that the senior Louisiana senator's popularity has eroded 16 points since February, with 52% now viewing him unfavorably.
In a further insult to Vitter, the Republican who came in fourth place -- Lt. Gov. Jay Dardenne - endorsed Edwards last week.
Publicly, Republican leaders are sounding supportive, saying they wouldn't entertain any questions about his future beyond next week's Louisiana election.
"I'm not willing to go there because I think he's going to win the governor's race," said Sen. John Cornyn of Texas, majority whip, when asked if he wanted Vitter to run for re-election.
Advisers close to Vitter say the argument is academic because the polling is inaccurate -- much the way it was in last week's Kentucky governor's race -- and predicting the GOP senator would emerge victorious. A Vitter spokesman didn't comment.
But privately, the assessment among many key Republicans is brutal.
"Let's face the facts: He can't win re-election to the Senate with these kind of numbers and with the difficult map that Republicans are facing, he could be a drain on the majority," said one Senate Republican operative.
'D.C. Madam' prostitution scandal returns
There is little dispute that the brutal campaign has taken a toll on Vitter.
The senator has had to repeatedly defend his character as his opponents have recited alleged indiscretions of his past, most notably in 2007 when he apologized for committing a "very serious sin" after his phone number was discovered during an investigation of a D.C. prostitution ring.
Edwards' campaign ad hitting Vitter on the prostitution scandal was doubly effective since the Democrat is a veteran.
"The choice for governor couldn't be more clear: John Bel Edwards, who answered his country's call and served as a ranger in the 82nd Airborne Division or David Vitter, who answered a prostitute's call minutes after he skipped a vote honoring 28 soldiers who gave their lives in defense of our freedom."
"David Vitter chose prostitutes over patriots," the ad says. "Now, the choice is yours."
At a Tuesday night debate, Vitter chastised Edwards for launching the "most vicious" negative ad of the campaign and "not living by the honor code," calling Edwards "very disingenuous."
The two talked over each other, hurling insults, with Edwards calling Vitter "a liar," a "cheater" and "a stealer."
"If it's a low blow, it's only because that's where you live, senator," Edwards said of the ad.
In the final days of the campaign, Vitter released an ad acknowledging the sex scandal.
"Fifteen years ago, I failed my family -- but found forgiveness and love. I learned that our falls don't define us, but rather how we get up, accept responsibility and earn redemption," Vitter said, looking into the camera. "You know me, I'm a fighter."
Candidates line up for 2016 race
Since the 2007 scandal, Vitter has mainly kept to himself in the Senate, and hasn't had a particularly good relationship with fellow Republicans. He rarely socializes with his colleagues, and typically leaves GOP lunches early. He angered many lawmakers from both parties by his repeated and unsuccessful efforts to eliminate federal contributions to subsidize lawmakers' and aides' health care coverage.
Regardless of what Vitter does, there are a number of potential Democratic and Republican candidates who could jump into the race next year. On the Democratic side, New Orleans Mayor Mitch Landrieu -- the brother of former Sen. Mary Landrieu, who had a contentious relationship with Vitter -- is seen as a possible candidate.
On the GOP side, Reps. John Fleming and Charles Boustany are potential candidates as is John Kennedy, the state treasurer, and Scott Angelle, the public service commissioner who came in third place in the gubernatorial primary.
The Republican map for staying in the majority is already daunting without having to worry about Louisiana. There are 24 GOP Senate seats to defend, compared to 10 for the Democrats, and Republicans need to lose no more than four to keep the majority if Democrats retain the White House.
Moreover, many Republican seats run through blue and purple states like Illinois, Wisconsin, New Hampshire, Florida and Pennsylvania -- something that will force the GOP to spend tens of millions of dollars to defend.
One senior Republican operative who works closely on Senate races said the last thing their party wants is to have vulnerable senators answering questions about Vitter's sex scandal.
"He's exactly what we don't need," the GOP operative said. "We need to drain the swamp."
At the beginning of the cycle, Vitter was viewed as a shoo-in for the governor's race. Sen. Roger Wicker, chairman of the National Republican Senatorial Committee said he expects that will be the outcome.
"He'll be the next governor," said Wicker, declining to entertain questions about Vitter's potential Senate reelection.