Former President Donald Trump is taking a side in Arizona’s combustible Republican Senate primary in the race to challenge first-term Democratic Sen. Mark Kelly in November.

The former president on Thursday endorsed Blake Masters, a venture capitalist and protégé of billionaire hedge fund giant Peter Thiel, who’s one of five GOP candidates running in the August 2nd primary in Arizona, a crucial general election battleground state that also borders Mexico.

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"Blake is Strong on Border Security, in particular, the disastrous Southern Border where people are pouring into the U.S. by the millions, and destroying our Country," the former president said in a statement issued by his Save America political action committee. "Additionally, he will Cut Taxes and Regulations, be Tough on Crime, and Support our Military and our Vets.  Blake will fight for our totally under-siege Second Amendment, and WIN!"

Trump’s endorsement of Masters comes as no surprise. 

Trump made an appearance at a Masters fundraiser at the former president’s Mar-a-lago Florida resort in November. And Trump called into a Masters campaign event in late April. There was speculation Trump would formally back Masters earlier this year, but the endorsement never materialized at the time.

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Trump is also increasingly in line with Thiel, the PayPal co-founder and tech billionaire who’s infused more than $13 million of his own money into a pro-Masters super PAC. Until March of this year, Masters ran Thiel Capital and the Thiel foundation. Trump in April — just ahead of the Ohio GOP Senate primary — endorsed another Thiel supported candidate who used to work for the billionaire, JD Vance. With the former president’s backing, Vance surged and won a very contested GOP primary battle.

"President Trump is a great man and a visionary. He saved this country from a Hillary Clinton regime and forever transformed American politics... and he’s not done yet," Masters said in statement. "It’s incredible to have his endorsement — I wish everyone could know how this feels"

Former President Donald Trump holds a rally sponsored by Save America with Ted Budd, Madison Cawthorn, Bo Hines, Dan Bishop, Mark Robinson and Greg Murphy in Selma, North Carolina, on April 9, 2022. (Photo by Peter Zay/Anadolu Agency via Getty Images)

Former President Donald Trump holds a rally in Selma, North Carolina, on April 9, 2022. (Photo by Peter Zay/Anadolu Agency via Getty Images) (Peter Zay/Anadolu Agency via Getty Images)

Masters is a strong proponent of the former president’s unproven claims that the 2020 election was riddled with massive voter fraud and rigged to deliver a false victory to President Biden. And Trump, in his statement, once again spotlighted his grievances.

"Arizona is a State where the 2020 Election was Rigged and Stolen, and a very thorough audit proved it," the former president charged. "Blake knows that the "Crime of the Century" took place, he will expose it and also, never let it happen again."

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And Trump once again took aim at Arizona Attorney General Mark Brnovich — one of Masters main rivals for the GOP Senate nomination — who in the days after the 2020 presidential election rejected Trump’s claims that election fraud was to blame for the then-president’s narrow loss to now President Biden in Arizona.

Arizona Attorney General Mark Brnovich says border crisis constitutes "invasion" under Constitution

Arizona Attorney General Mark Brnovich, in a Fox News interview. (Fox News)

Brnovich last year launched a probe after Republican state Senate President Karen Fann urged him to investigate the findings of a controversial ballot review that she and other GOP state senators conducted last year of the more than two million votes cast in Maricopa County, the state’s largest county.

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"Mark Brnovich is such a disappointment to me," Trump said in his statement. And the former president claimed that Brnovich "does not support clean and fair elections, or law and order, and could not properly represent the people of Arizona in the United States Senate."

Jim Lamon, a solar power businessman who’s poured millions of his own money into his Senate bid, retired Major Gen. Mick McGuire, the former Adjutant General of the Arizona National Guard, and Justin Olson, a member of the Arizona Corporation Commission, are also running for the Republican nomination.

Lamon's been running an ad that attacks Masters as a "puppet" of Big Tech, referring to his close relationship to Thiel.

Sen. Mark Kelly of Arizona at southern border

Sen. Mark Kelly of Arizona (at left) meets with U.S. Customs and Border Protection officials at the Douglas Port of Entry along the U.S.-Mexico border, on April 13, 2022 (Sen. Mark Kelly office)

The winner of the GOP primary will face off with Kelly, the former astronaut who in 2020 won a special election to fill the final two years of the term of the late GOP Sen. John McCain. While the Democrats face historical headwinds and a very unfavorable political climate as the midterm elections near, beating Kelly in the purple state won’t be easy.

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Kelly has hauled a massive $39 million in fundraising so far this election cycle and had a formidable $23.2 million in his campaign coffers as of the end of March.