Bredesen, a Democratic former mayor of Nashville, served two terms as governor of Tennessee from 2002 to 2010. If he manages to flip Corker's seat -- and if Democrats can win seats in Arizona and Nevada and reelect most of their vulnerable senators -- they could eke out a Senate majority in 2018.
But could Bredesen, whose state has taken a sharply conservative turn since he left the governor's mansion, win statewide office as a Democrat?
For guidance, we looked at 16 former governors who have sought U.S. Senate seats during the current millennium. Overall, 11 of these candidates won and five lost, for a winning rate of 69 percent.
The winners include Democrats Tom Carper of Delaware, Jeanne Shaheen and Maggie Hassan of New Hampshire, Joe Manchin of West Virginia and Tim Kaine of Virginia. On the Republican side, they include Lamar Alexander of Tennessee, Mike Johanns of Nebraska, Jim Risch of Idaho, John Hoeven of North Dakota and Mike Rounds of South Dakota. And lastly, independent Angus King of Maine.
But while the list is impressive and the rate of victory promising, that overall record obscures some distinctions between the winning and losing candidates. What's more, Bredesen's profile looks more like the candidates who lost.
If he does end up losing his bid, he'll join Republicans Jim Gilmore of Virginia and Linda Lingle of Hawaii, and Democrats Bob Kerrey of Nebraska, Ted Strickland of Ohio and Evan Bayh of Indiana. (Kerrey and Bayh were one-time governors who actually won Senate seats, retired and then failed in comeback bids for the Senate.)
Two metrics stuck out as having influenced these failed Senate campaigns.
Does Distance Make the Heart Grow Fonder?
One was the amount of time that had elapsed between the candidate's departure from the governorship and their Senate bid. The second factor was whether the candidate was running in a state that, at the time of their Senate run, was generally favorable to their party in statewide races.Among the 11 winners, only two had been out of office for more than six years -- Alexander and King. Alexander had been out of the governorship for 16 years (though he had served as a cabinet member and run for president in the interim), and King had been out for 10 years.
Carper, Hassan, Hoeven and Manchin, on the other hand, actually ran for Senate while still in the governor's mansion, and the others had been out of office from between two and six years when they won their Senate seat.
Meanwhile, almost all the winning candidates ran in states that tilted strongly toward their party. The main exception was Manchin, who won in a state that by 2010 was heading sharply toward the GOP.
Among the five governors who lost, Lingle had been out for the shortest amount of time -- two years. Otherwise, Strickland had been away from the governorship for six years, Gilmore for seven years, Bayh for 20 years and Kerrey for 26 years. Bayh and Kerrey had similarly been out of the Senate for several years -- Bayh for six and Kerry for 12 -- before attempting to return.
All told, a longish time out of office appears to have hurt these candidates' chances. The partisan leanings of their states clearly hurt, too.
Two of the losing candidates, Gilmore and Strickland, were running in purple states. But the others were running in distinctly unfriendly territory: Kerrey and Bayh as Democrats in red states, and Lingle as a Republican in a blue state.
Them and Him
So how does Bredesen compare on these metrics?For starters, he's a Democrat running in a solidly red state. And he's been out of the governorship for eight years -- a profile more like the historical losers than the winners.
One of the reasons a candidate's time out of office matters, of course, has to do with the difficulty of maintaining ties to voters and keeping one's political skills fresh. Another part has to do with explaining what they've been doing since leaving elective office.
In Kerrey's case, for instance, "he spent a decade living in New York as the president of the New School," says Randall E. Adkins, a University of Nebraska Omaha political scientist. "During that time, he didn't maintain a home in Nebraska nor had he really spent much time in the state, which made it easy for his opponents."
As for the significance of the state's partisan leanings, that seems obvious. But it is important to note that it's especially important for Senate seats because they garner more national attention and inevitably become more partisan than gubernatorial races.
For Lingle, "voters in this deep-blue state [might have been] willing to cross party lines to elect a proven administrator, a former county mayor, as governor," says Hawaii journalist Nancy Cook Lauer. But the state "hasn't sent a Republican to the U.S. Senate since 1970, and having native son Barack Obama on the top of the ballot for his second term that year certainly didn't hurt Democratic chances."
Of course, other factors can contribute to a loss.
"With the possible exception of Lingle, these candidates lost more because they ran lousy campaigns as opposed to anything they did as governor," says Jennifer Duffy, who handicaps Senate and gubernatorial races for the Cook Political Report.
Strickland, for instance, had a rough term as governor during the Great Recession and failed to win reelection. He started with good poll numbers, but allies of his opponent, Republican Rob Portman, "ran negative ads on how bad the economy and the state budget was during his term," says Bill Binning, a former Republican official in Ohio and professor emeritus at Youngstown State University.
Back in Tennessee, political observers understand the risks Bredesen faces.
"I do think that Bredesen is vulnerable to the same forces that hamstring former governors who run for federal office," says University of Tennessee political scientist Anthony Nownes. "And this state is, in my opinion, even more conservative now than it was when Bredesen was government. He faces an uphill climb."
That said, Nownes and others suggest it's far too early to write off Bredesen.
For one, Democrats nationally are poised to have a strong midterm election this year, thanks to a backlash against President Trump. Observers in Tennessee also suggest that Bredesen has insulated himself in ways that Kerrey, Bayh and others did not.
"Bredesen still has standing in the state, and he will run as a problem-solver, not as a Democrat," says Vanderbilt University political scientist John Geer. Bredesen is a credible moderate, he says, and his potential GOP opponent, U.S. Rep. Marsha Blackburn, "is vulnerable to being labeled a Washington insider."
Nownes adds that Bredesen also benefits from widespread name recognition and, unlike Strickland, was popular when he was governor. "No one has particularly negative feelings toward him."
Meanwhile, former Republican Minnesota Gov. Tim Pawlenty is also considering a U.S. Senate bid this year. If he runs, the outlook for Pawlenty compared to Bredesen might be somewhat less ideal.
Observers say that even when Pawlenty won the governorship, he benefited from having Jesse Ventura's old Independence Party on the ballot, allowing him to win with less than a majority of the popular vote. With the Independence Party now essentially defunct, that won't be the case in 2018.
More important, Pawlenty shares an out-of-state drag with Kerrey and other losing candidates.
"Pawlenty has been gone for a while as a well-compensated D.C. lobbyist," says Carleton College political scientist Steve Schier, "and that could be a problem for him in returning to run for Senate here."
*After we published this story, two readers pointed out that we missed a few former governors who ran for the U.S. Senate after 2000. Ronnie Musgrove, a Democrat running in solidly Republican Mississippi, lost a special Senate election five years after losing reelection as governor. Charlie Crist, then a Florida Independent, ran while serving as governor and lost. And Tommy Thompson, a Wisconsin Republican, ran for a Senate seat 12 years after he left the governor's office and lost.
