Updated at 6:49 p.m. on Monday, Sept. 17, 2018, with more information.

NASHVILLE — A CNN poll released Monday places Democrat Phil Bredesen with a 50-45 percent lead over Republican Marsha Blackburn in Tennessee's U.S. Senate race.

The SSRS survey of 723 likely voters, conducted Sept. 11-15, has a margin of error of plus or minus 4.3 percent.

Bredesen, a former governor and one-time Nashville mayor, and Blackburn, a Brentwood congressman, are squaring off to succeed retiring Republican Sen. Bob Corker of Chattanooga.

It's shaped up so far as Tennessee's fiercest Senate battle since Corker narrowly beat Democrat Harold Ford in 2006. Blackburn, Bredesen, national parties and independent expenditure groups are throwing millions of dollars into ads in the Nov. 6 election an effort to sway voters in a key state that could determine Senate control.

Marsha Blackburn and Phil Bredesen

CNN reported the poll found voters' positive views of Bredesen, who enjoyed high ratings as governor, are more than double his negatives. Fifty-five percent of likely voters said they viewed him favorably and 26 percent in a less favorable light. Ten percent had no opinion, while nine percent said they'd never heard of him.

But it was much closer for Blackburn in the CNN poll. Voters' favorable and unfavorable views were tight. Forty-five percent told pollsters say they view Blackburn favorably while nearly as many, 43 percent, said they see her unfavorably. Nine percent had no opinion, and just three percent said they hadn't heard of her.

A Sept. 8-11 Fox News poll released last week showed Blackburn narrowly leading Bredesen among likely voters by 47 percent to 44 percent, a 3-point margin that is within that survey's margin of error.

In Tennessee's governor race, the new CNN poll found Republican Bill Lee leading Democrat Karl Dean by nine points, with 52 percent saying they viewed Franklin businessman Lee favorably compared to 43 percent who viewed former Nashville mayor Dean favorably.

The Fox poll found a 20-point spread between the two gubernatorial candidates, with voters likely to back Lee by 55 percent to 35 percent for Dean. But it also had a higher number of undecided voters.

CNN's poll, meanwhile, found Tennessee likely voters evenly divided over President Donald Trump's handling of his job as president. Forty-nine percent approved while 48 percent disapproved.

Fox's poll found Tennessee voters approve of the job Trump is doing by a 58-38 percent margin. Thirty-five percent said in the Fox poll their vote in the Senate contest will be to express support for the president, while 27 percent said it would be to voice opposition.

An Aug. 25-28 NBC News poll showed a similar nail-biter of a contest with Bredesen slightly ahead. Forty-eight percent of likely voters said they supported Bredesen, while Blackburn garnered 46 percent.

Blackburn campaign spokeswoman Abbi Sigler said "we've always known this is going to be a tight race. Bredesen's campaign is bought and paid for by Chuck Schumer. He donated $33,400 to Hillary Clinton, and he wanted Tennesseans to roll up their sleeves and work for her to be our president.

"Tennesseans want a conservative in the Senate, and they know Marsha is the only candidate in the race who will represent their values," Sigler said.

Trump won Tennessee in 2016, beating Democrat Hillary Clinton by 26 points. But a number of political observers here say Bredesen, who has said he would serve as a moderate pragmatist and is not reflexively opposed to Trump or Republicans on everything, is not your average Democrat.

Calling Bredesen a "very formidable Democrat," a top reporter for the conservative Washington Examiner said earlier this month in a panel discussion on CNN's "Inside Politics" that he thinks of Bredesen as something of a "unicorn candidate because he's so well-liked in Tennessee, which has become so Republican, even though he's a Democrat."

Differences in the poll could perhaps be attributable to several factors, including what's happening in the news when polls are taken, the onslaught of attack ads or methodological differences among polling firms.

The Tennessee Journal, a respected follower of state politics, reported that the Fox sample included 53 percent Republicans, 35 percent Democrats and 12 percent independents. The survey was a joint effort by Shaw & Company, a Republican firm, and Anderson Robbins, a Democratic firm.

CNN's description of SSMS's methodology shows 26 percent of those surveyed described themselves as Democrats, while 33 percent identified with Republicans. Forty percent described themselves as independents or members of another party.

The NBC/Marist College poll's methodology has 35 percent of those surveyed as Republican, 29 percent Democratic and 35 percent independent.

Contact Andy Sher at asher@timesfreepress.com or 615-255-0550. Follow on Twitter @AndySher1.