Former President Donald Trump's sway over the Republican Party is on the line on Tuesday in a Republican Senate primary runoff election in Alabama and two GOP congressional runoffs in neighboring Georgia.

The biggest prize is in deep red Alabama, where the primary run-off winner will be the heavy favorite in November’s general election in the race to succeed Republican Sen. Richard Shelby, who’s retiring after nearly 45 years in Congress.

Katie Britt, a former longtime Shelby aide who served as the senator’s chief of staff from 2016-2018 and who later became the first female president and CEO of the Business Council of Alabama, is considered the favorite in the Alabama runoff, against Rep. Mo Brooks, who was one of Trump’s top allies in the House.

Trump backed Brooks last year when the congressman was the front-runner in the race, but the former president took back his endorsement earlier this year as Brooks struggled in the polls. And after criticizing Britt last year, Trump praised her as he endorsed her a week ago, after new polls indicated Britt surging.

BRITT AND BROOKS BATTLE FOR GOP SENATE NOMINATION IN DEEP RED ALABAMA

Katie Britt Mo Brooks runoff

Senate candidates Katie Britt (L) and Mo Brooks (R) (Andi Rice, Bloomberg via Getty Images / AP Photo, Vasha Hunt)

The winner of the runoff election will be considered the clear front-runner in November’s midterms against Democratic nominee Will Boyd, a pastor and former Democratic Party county chair who’s considered a perennial candidate.

Trump is also taking sides in Georgia’s two congressional runoffs.

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In the 6th Congressional District, which covers mostly rural regions north of Atlanta, the former president is backing Jake Evans, a former chairman of the Georgia Ethics Commission and son of Randy Evans, who served as ambassador to Luxembourg during the Trump administration. The former president headlined a tele-rally for the younger Evans on the eve of the primary.

The other candidate in the race, physician Rich McCormick, is supported by conservative firebrand Sen. Ted Cruz of Texas, as well as the Club for Growth, a fiscally conservative outside group that spends heavily in Republican primaries.

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This is the third high profile Republican primary showdown the past two months where Trump and Cruz — who could become potential rivals in the 2024 GOP presidential nomination race — have backed rival candidates in Republican primaries.

The winner of Tuesday’s GOP primary runoff will face off in November against Democratic nominee Bob Christian, a veteran. The current incumbent, Democratic Rep. Lucy McBath, is running for re-election this year in Georgia’s 7th Congressional District, after the seat was redrawn in the once-in-a-decade redistricting process to heavily favor Republicans.

GEORGIA GOV. KEMP ENDORSES MIKE COLLINS OVER TRUMP-BACKED VERNON JONES

In Georgia’s 10th Congressional District, Trump is supporting Vernon Jones, a former state lawmaker and Democrat turned Republican who was a top Black surrogate for the then-president in the Peach State during the 2020 election. Jones is facing off on Tuesday against Mike Collins, the owner of a trucking company.

Either Collins or Jones will be considered the favorite against the winner of the Democratic primary runoff in the district, in the race to succeed Republican Rep. Jody Hice, who launched an unsuccessful campaign for Georgia secretary of state rather than seek re-election.

Collins was endorsed last week by Republican Gov. Brian Kemp, just three weeks after Kemp crushed former Sen. David Perdue, who was primary challenging the conservative governor with heavy support from Trump. Kemp topped Perdue by more than 50 points in last month’s Republican gubernatorial primary, which was a stinging defeat for Trump. Kemp had raised Trump’s ire for certifying the then-president’s razor-thin electoral defeat to now-President Biden in Georgia in the 2020 election.

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Perdue wasn’t the only high-profile Trump-backed candidate to go down to defeat in Georgia’s primary. Hice lost by double digits to Secretary of State Brad Raffensperger, whom Trump had also repeatedly attacked. And Trump backed GOP attorney general challenger John Gordon was demolished by incumbent Chris Carr.

Jones was originally running for governor this cycle, in hopes of landing Trump’s endorsement in the primary against Kemp. But after he endorsed Perdue, the former president convinced Jones to end his gubernatorial bid and instead run for Hice’s open congressional seat. Trump endorsed Jones as he launched his House bid.

The District, which is reliably red, stretches from the exurbs east of Atlanta through rural areas east to the outskirts of August and to the South Carolina border. 

"Trump’s ire has outweighed his influence in Georgia," veteran Georgia based Republican consultant Dan McLagan said. And pointing to the large slate of candidates Trump endorsed in Georgia’s primary, he noted "if you bet on six horses to win the Kentucky Derby, you’re guaranteed to lose five of them. And Trump wasn’t strategic picking his horses."

"Vernon’s about to learn that if you shoot at the king, you better not miss," McLagan argued. "Kemp’s stock in Georgia is a lot higher than Trump’s right now."

It's also primary day in Virginia, where Republican candidates in the state’s 2nd and 10th Congressional Districts are vying to face off in November with two House Democrats who face challenging reelections as their party up against historical headwinds and a very difficult political climate.

Four Republicans — who are all veterans — are running in the very competitive 2nd District, a seat in southeastern part of the commonwealth that’s anchored by Virginia Beach. Among them is state Sen. Jennifer Kiggans, the only one to have held elected office.

The winner will face off in November against Rep. Elaine Luria, a former U.S. Navy commander turned two-term Democratic congresswoman. Luria has been very visible this month, as the House Select Committee investigating the Jan. 6, 2021 attack on the U.S. Capitol has been holding high profile hearings that have grabbed national attention. Luria is the only endangered Democrat sitting on the panel.

In the newly drawn 7th District, which was heavily shifted by redistricting and will now stretch from the Fredericksburg area north toward Washington D.C.’s southern suburbs — including portions of heavily populated Prince William County — six Republicans are vying to challenge former CIA officer turned two-term Democratic Rep. Abigail Spanberger.

Among the GOP candidates is Yesli Vega, a military wife, mother and law enforcement officer born to Salvadoran immigrants after they fled civil war.

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In the heavily blue 8th Congressional District – located in the Virginia suburbs of the nation’s capital — former lt. governor and four-term Rep. Don Beyer’s facing a primary challenge from progressive Victoria Virasingh. 

And in the deep red 6th Congressional District, which covers much of the west-central portion of Virginia, GOP Rep. Ben Cline is facing a primary challenge from former Navy officer and political newcomer Merritt Hale.

Fox News' Jessica Loker contributed to this report