NASHVILLE (AP) — Four candidates who have spent tens of millions of dollars of their own wealth fighting over who is more devoted to President Donald Trump face off Thursday in the Republican primary for Tennessee governor.

Meanwhile, former Democratic Gov. Phil Bredesen and Republican U.S. Rep. Marsha Blackburn face only nominal primary opposition in their high-profile race to replace retiring Republican Sen. Bob Corker, one of several contests that could decide control of the Senate.

The state, like its southern neighbors, was once dominated by Democrats. But it hasn't elected one to statewide office since 2006, and in 2012 Republicans secured supermajorities in both houses for the first time since Reconstruction. Tennessee favored Trump by 26 percentage points in 2016.

The contest to succeed popular term-limited Republican Gov. Bill Haslam has attracted four leading Republicans: U.S. Rep. Diane Black, former state economic development chief Randy Boyd, businessman Bill Lee and state House Speaker Beth Harwell. Together, they have put some $40.2 million of their own money into the race and have spent a record $45.7 million total.

With the spending spree, the candidates have fought over who is more loyal to the president and his tough-on-immigration priorities.

Vice President Mike Pence has offered his support for Black. But Trump has stopped short of endorsing her, despite keeping her by his side and praising her during several events.

Two leading Democrats have been far more cordial in their race for their party's nomination. Former Nashville Mayor Karl Dean has outspent state House Minority Leader Craig Fitzhugh $4.4 million to $984,800, though Fitzhugh has peeled off important endorsements from state employees' and teachers' groups.

Both candidates argue they are leaders who can break down partisan barriers and make divided government work during divisive political times — messaging that points to the tightrope Democrats must walk to get elected statewide in Tennessee.

Any Democratic nominee for either governor or senator would need the support of moderate Republicans and independents.

Bredesen was the last Democrat to pull that off, winning all 95 counties in his 2006 gubernatorial re-election. Blackburn has aligned herself strongly with the White House and held public events in Tennessee with Trump and Pence.

For months, Bredesen and Blackburn have looked beyond the primary and campaigned as if the general election had already started.

A general election win would be historic for either Black or Blackburn, since the state has never elected a woman as governor or U.S. senator.

Their bids for higher office, as well as the retirement of Knoxville Republican Rep. John Duncan Jr., have cleared the way for competitive, open contests in three of the state's nine U.S. House seats.

Harwell and Fitzhugh's decision to run for governor means the top leadership spots in both parties at the General Assembly will be up for grabs next year, even as new members will be elected to replace 18 Republicans and seven Democratic incumbents who aren't seeking re-election in the House. In addition, two Democrats and one Republican in the Senate are retiring.