A bitter and expensive Tennessee gubernatorial primary comes to a close Thursday as Republicans will officially choose who will be their party's nominee.

The top four GOP contenders have emerged as a congressman, state House speaker, local businessman and political outsider: Rep. Diane Black, state Rep. Beth Harwell, former state economic development commissioner Randy Boyd and Bill Lee.

The four added $33 million in combined personal wealth to their campaigns and spent about that much, setting records and more than doubling what they've raised through donations.

Current Gov. Bill Haslam, a Republican, is term limited.

In the tense primary, the Republicans all share at least one commonality: loyalty to President Trump and his policies. Trump won Tennessee with more than 60 percent of the vote in the 2016 presidential election.

Read on for a look at the GOP frontrunners ahead of Thursday's primary.

Diane Black

Rep. Diane Black announced her candidacy for governor exactly a year before the primary date. Touting her conservative record, Black promised not to “back down” when she announced she was throwing her hat into the ring.

Black, 67, has represented Tennessee’s 6th congressional district since 2011. She’s a registered nurse and small businesswoman – and was first in her family to earn a college degree.

In the House, Black chaired the powerful Budget Committee for a year, stepping down to pursue the governorship. She also serves on the Ways and Means Committee.

If elected, Black promises to lead Tennessee in favor of gun rights and against abortion. She also said she wants to “lead the charge to shut down motel and massage parlors operating as dens of human trafficking” in the state.

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Black has earned the endorsement of Vice President Mike Pence. Trump hasn’t formally backed anyone in the race, but he did say “good luck” to her while at a Nashville rally for Rep. Marsha Blackburn, a Senate candidate, in May.

She has been endorsed by former Pennsylvania Sen. Rick Santorum, the American Conservative Union and the National Rifle Association.

Black is the only candidate in the race who has served at the federal and state level, WBIR-TV reported.

Considered to be an early frontrunner, Black has sought to balance her time in Washington, D.C., with how she would govern the state, according to The Tennessean. She’s been an ardent supporter of Trump and has introduced legislation that aligns with his agenda, including crowdfunding a border wall and designating illegal border crossing a felony.

Randy Boyd

Businessman Randy Boyd was one of the first to announce his intentions to run for governor.

Aside from being CEO of Radio Systems Corp., the parent company of several pet products, including PetSafe and Invisible Fence, Boyd also helped start a state program that provides free community college as well as partners mentors with high school graduates, according to his campaign website.

Boyd, 58, also served as an unpaid adviser on education for Haslam and was Tennessee’s Economic and Community Development Commissioner for two years. As commissioner, Boyd helped to bring in almost $11 billion in capital investments to Tennessee as well as 50,000 new job commitments, The Tennessean reported.

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As governor, Boyd said he wants to be “chief salesman” for the state and continue to push for a better economy and education, which includes a focus on technical trainings.

To campaign, Boyd has jogged – literally – across part of Tennessee.

Former Arkansas Gov. Mike Huckabee endorsed Boyd in June, comparing him to the president while doing so.

Huckabee said Boyd has “spent his life building a company from scratch, and like President Trump, he knows what it takes to disrupt government-as-usual.”

Boyd has also been backed by more than 120 county and city mayors and more than 50 law enforcement leaders, his campaign said.

Beth Harwell

Calling herself a “Ronald Reagan Republican,” Beth Harwell has led the Tennessee House as speaker since 2011. In that role, she has been instrumental in ensuring Tennessee is one of the lowest taxed states, balancing the budget every year and fostering a business-friendly environment, according to her campaign website.

“As governor, I will lead on jobs, cutting taxes, guaranteeing every child has a great school and ensuring our Tennessee values are protected,” Harwell, 61, said when she announced her candidacy last year.

Harwell is also anti-abortion and a gun rights advocate.

Harwell, too, is a Trump supporter and told Fox News her goals as speaker mirror that of Trump’s in the White House: lowering taxes, ending sanctuary cities and alleviating debt.

“I believe I have the proven performance and results that conservatives in the state of Tennessee want,” she said in contrasting her record with her opponents.

She also credited “a lot of” Haslam’s legislative achievements to her speakership.

According to her House biography, Harwell has pushed for stronger sexual abuse laws and victims’ rights, including increasing jail time for convicted rapists.

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She’s been honored with the Guardian of Small Business Award from the National Federation of Independent Businesses twice. The Tennessee Education Association Fund for Children and Public Education, the state’s teacher PAC, endorsed Harwell in May.

She’s the only candidate who supports the legalization of medicinal marijuana, according to The Associated Press.

Bill Lee

As the only candidate without a political background, businessman Bill Lee has cast himself as an outsider in the race, which he has described as a “calling.”

If elected, Lee, 58, would focus on jobs and rural communities as well as boosting the state’s education system while cracking down on illegal immigration. Like his GOP opponents, he is also a defender of gun rights and is anti-abortion.

Lee’s first wife died in a horseback riding accident, and although he’s since remarried, he hasn’t shied away from talking about how her death impacted his outlook on life and business.

At the time, his family air conditioning business was successful, but he decided to take a step back from it, appointing a new CEO, to spend time with his children, The Tennessean reported.

“My entire life had turned upside down, and I didn’t much care about anything that I’d previously cared about for a short period of time, and that’s what disarray will do for you,” Lee told the newspaper. “I cared about my family, and that was my primary goal at the time.”

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After her death, he started working at a program geared toward at-risk youth and the Men of Valor, an organization that helps men who have been released from prison readapt into society, The Tennessean reports.

According to his campaign website, Lee Company now garners an annual revenue of $215 million, has won numerous awards and employs more than 1,200 people.

Lee also works with his family’s large cattle farm, according to his campaign website.

Nashville Predators captain Mike Fisher and NASCAR great Darrell Waltrip are “honorary co-chairs” on Lee’s campaign.

The Associated Press contributed to this report.