Republican House, Senate and gubernatorial hopefuls are gearing up for Tennessee’s primaries on Thursday, the first in a series of races this month that will help shape the critical 2018 midterms.

The primary to watch is the Republican gubernatorial race, where Rep. Diane Black Diane Lynn BlackBottom line Overnight Health Care: Anti-abortion Democrats take heat from party | More states sue Purdue over opioid epidemic | 1 in 4 in poll say high costs led them to skip medical care Lamar Alexander's exit marks end of an era in evolving Tennessee MORE (R) is fending off a slew of strong challengers in the race to succeed term-limited Republican Gov. Bill Haslam.

Tennessee will also hold a slew of competitive Republican House primaries on Thursday. The Senate primaries are contested both on the Democratic and Republican side, but former Governor Phil Bredesen (D) and Rep Marsha Blackburn Marsha BlackburnHillicon Valley: Subpoenas for Facebook, Google and Twitter on the cards | Wray rebuffs mail-in voting conspiracies | Reps. raise mass surveillance concerns Key Democrat opposes GOP Section 230 subpoena for Facebook, Twitter, Google Senate panel threatens subpoena for Google, Facebook and Twitter executives MORE (R) have emerged as overwhelming favorites in their respective races to replace retiring Sen. Bob Corker Robert (Bob) Phillips CorkerHas Congress captured Russia policy? Tennessee primary battle turns nasty for Republicans Cheney clashes with Trump MORE (R).

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Gubernatorial race

Diane Black, the former chairman of the House Budget Committee, has seen her lead erode in a race that has attracted millions of dollars.

President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE, whose endorsements have been critical in Republican primaries so far, has stayed out of the primary, but Vice President Mike Pence Michael (Mike) Richard PencePence vows for law and order everywhere Trump met with chants of protest as he pays respects to Ruth Bader Ginsburg The Hill's 12:30 Report: Ginsburg lies in repose MORE has come out in support of Black.

Black is facing off against businessman Randy Boyd, who has spent a whopping $21.07 million on the race. State House Speaker Beth Harwell and cattle farmer Bill Lee - who has seen a fundraising surge in recent weeks - are also contenders.

The gubernatorial primary is seen as an open race. While Black was once the leading contender, a recent poll from JMC Analytics and Polling had Lee in first place with 26 percent, with Boyd in second at 20 percent and Black not far behind with 19 percent.

Senate race

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Rep. Marsha Blackburn is set to face off against trucker Aaron Pettigrew in the Republican primary race to replace Corker.

A prominent conservative voice in the House who was first elected to the House in 2002 after serving in the state legislature, Blackburn is the overwhelming favorite, with far more name recognition. She’s received an endorsement from President Trump, with whom she has a close working relationship after serving on his transition team.

The winner of the GOP primary will likely face Bredesen who is widely expected to win the Democratic primary against two lesser known challengers, Gary Davis and John Wolfe.

The Blackburn-Bredesen race is seen as a must-win race for both Republicans and Democrats in the fall. The race is rated as a “toss-up” by The Cook Political Report even though Democrats haven’t won a Senate seat in Tennessee in nearly 30 years.

Corker has said he won’t campaign against Bredesen and offered only a lukewarm endorsement for Blackburn.

House District 2

Seven Republicans are vying to replace long-time Rep. John Duncan John James DuncanLamar Alexander's exit marks end of an era in evolving Tennessee Tennessee New Members 2019 Live coverage: Social media execs face grilling on Capitol Hill MORE Jr. (R), who is set to retire at the end of this term.

State Rep. Jimmy Matlock, who has Duncan’s endorsement in the race, and Bigfoot hunter and Knox County Mayor Tim Burchett are currently seen as the top contenders.

Military pilot Ashley Nickloes is the only female in the crowded field and had the support of groups including Main Street Republicans.

The other candidates seeking the GOP nomination are Jason Emert, who previously worked as a staffer for Sen. Lamar Alexander Andrew (Lamar) Lamar AlexanderGraham: GOP has votes to confirm Trump's Supreme Court nominee before the election The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy This week: Supreme Court fight over Ginsburg's seat upends Congress's agenda MORE; Army veteran Hank Hamblin; Navy veteran Vito Sagliano; and David Stansberry, another Army vet and minister.

House District 6

Retired judge Bob Corlew is facing John Roes, a farmer and former Tennessee Agriculture Commissioner in the Republican primary for the chance to replace Rep. Diane Black, who is running for governor.

Rose has attempted to paint Corlew as a career politician, while Corlew has also gone after his main opponent for being too close to “the swamp,” the Post Bulletin reports.

State Rep. Judd Matheny, who has been endorsed by the conservative House Freedom Caucus, is also seeking to be the GOP nominee.

House District 8

GOP Rep. David Kustoff David Frank KustoffLobbying world Trump announces, endorses ambassador to Japan's Tennessee Senate bid GOP to launch discharge petition on anti-BDS measure MORE, who has served only one term in the House, is facing a serious primary challenger in Dr. George Flinn, a perennial candidate who has spent upwards of $2.5 million in the race.

Trump has come out in support of Kustoff on two separate occasions. The president’s endorsement has propelled Republicans to victory in a handful of primaries, including more recently Georgia Secretary of State Brian Kemp, who defeated Lt. Gov. Casey Cagle.