Sen. Lamar Alexander’s (R-TN) announcement on Monday that he will not seek re-election to a fourth term to the U.S. Senate in 2020 is certain to launch a political free-for-all over the next year and eleven months in Tennessee to replace him.

The battle to succeed Lamar Alexander will be determined in the August 2020 Republican primary in this very red state that Donald Trump won by 26 points in 2016.

The Democrats’ best statewide hope since 2006, former Democrat Gov. Phil Bredesen, was trounced by Rep. Marsha Blackburn (R-TN-07) in the 2018 Senate election by 11 points, despite spending $7 million of his own money and receiving more than $12 million in support from Senate Minority Leader Chuck Schumer’s (D-NY) PAC.

Two names — each representing different elements of the Tennessee Republican Party — head the list of likely replacements for Alexander.

Representing the moderate “establishment” wing of the party — largely from East Tennessee — is Gov. Bill Haslam, who leaves office with strong approval ratings despite supporting a controversial gas tax increase after two terms in office in January.

Representing the conservative populist wing of the party is Rep.-Elect Mark Green (R-TN-07), a member of the Tennessee State Senate who easily won the Middle Tennessee seat in the House of Representatives that Rep. Blackburn left to run successfully for the Senate.

Sen. Lamar Alexander promised last month to announce whether he would seek re-election before the end of the year. His decision not to seek re-election, he said on Monday, was actually made several months ago.

“In a sit-down interview with News 2 hours after his announcement, Alexander said he decided several months ago not to seek re-election,” WKRN reported on Monday morning:

“Actually, I decided this in August when I was fishing in Canada,” he said, adding, “I wanted to keep it to myself to make sure it’s the right decision and I have decided that it is. It’s somebody else’s turn … this is the right decision for me, and I think Tennessee.”

Alexander said President Donald Trump just learned of his decision on Sunday night.

“He said, ‘Well, let’s talk about you serving another 20 years.’ And I said, ‘Mr. President, I am going to announce tomorrow I am not running,’ and he said, ‘Why would you do that?’ And we talked about it,” Lamar said.

Alexander also gave the potential candidacy of Haslam a boost on Monday, as WKRN’s Chris Bungaard tweeted:

If Gov. Haslam decides to make a run, he would automatically become the presumptive frontrunner, benefiting not only from his two terms as governor, but also from his estimated $2 billion in personal wealth, almost all of which derives from his ownership in Pilot Flying J, the company founded by his father, Jim Haslam, which is the fourteenth largest privately traded company in the country.

The Pilot Flying J connection is not without a downside, however, due to recent federal investigations on charges of overbilling that resulted in the arrest and conviction of former company president Mark Hazelwood on felony charges of conspiracy to commit wire fraud and witness tampering. Hazelwood’s boss, company CEO Jimmy Haslam, is Gov. Bill Haslam’s older brother.

Jimmy Haslam, who also owns the NFL’s Cleveland Browns, has, so far, not been touched by the financial scandal that sent Hazelwood and several other former Pilot Flying J executives to prison.

Haslam, a former mayor of Knoxville, has had only one contested race in his political career — the 2010 GOP Republican primary for governor — in which the well-financed, middle-of-the-road Haslam faced off against two less well-funded conservatives — former Rep. Zach Wamp (R-TN-02) and former Lt. Gov. Ron Ramsey.

As has happened many times in Tennessee, the two conservatives split the vote, allowing the middle-of-the road Haslam to secure the victory.

It is unclear if Haslam has the “fire in the belly” to take on a potentially tough political primary battle, as the 2020 race most certainly will be.

For his part, Green — while popular among the conservative populists who dominate the Republican Party — has yet to be sworn in to his seat in the House of Representatives.

Should he decide to run, Green would have to announce his candidacy just months into his first term in Congress.

Green, a graduate of the U.S. Military Academy who served in Iraq, made headlines in 2017 when he was nominated by President Trump to serve as Secretary of the Army, but he withdrew after strident criticism from groups who objected to his strongly pro-Christian views.

Other potential GOP candidates are former Tennessee Economic Development Commissioner and current U.S. Ambassador to Japan Bill Hagerty, outgoing Rep. Diane Black (R-TN-06), former gubernatorial candidate and entrepreneur Randy Boyd, and Vanderbilt orthopedic surgeon Manny Sethi.

Sethi, a medical colleague at Vanderbilt of former Sen. Bill Frist (R-TN), announced last week that he was considering a race for Republican nomination for the U.S. Senate in the event Sen. Lamar Alexander chose not to run for re-election. Well respected in the Nashville medical community, Sethi has the disadvantage of low name recognition and lacks the personal fortune of other potential candidates to bankroll his campaign, such as Gov. Haslam, Ambassador Hagerty, and Rep.-Elect Green.

Two possible candidates with considerable personal fortunes — Rep. Black and Randy Boyd — spent over $20 million each in their unsuccessful bids to win the Republican nomination for governor this year and damaged their brands among Republicans in the state with negative attacks against each other that allowed the underdog who took a positive messaging approach, Williamson County businessman Bill Lee, to slip through and easily win the GOP nomination in August.

Black seems unlikely to enter the political arena again, but Boyd, who was recently named as the interim president of the University of Tennessee, may still harbor political ambitions.

Like Alexander and Haslam, Boyd is an East Tennessean in the moderate establishment faction of the GOP, and he is unlikely to run in the event Haslam chooses to do so.

Though other potential challengers may emerge, the one most likely to break into the top tier should he decide to run is Ambassador to Japan Bill Hagerty.

A graduate of Vanderbilt Law School, Hagerty worked for Boston Consulting Group before serving as a White House Fellow under President George H.W. Bush. Hagerty went on to a successful career in investment banking before heading up Mitt Romney’s 2008 fundraising operations, serving as Bill Haslam’s Commissioner of Economic Development, playing a key role in President Trump’s 2016 fundraising operations, and heading up President Trump’s transition team.

Hagerty also can bridge the gap between the establishment Haslam faction of the Tennessee GOP and the populist conservative Trump faction.