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Republican Josh Mandel, a former Ohio state treasurer and Marine veteran who served in the Iraq war, on Wednesday became the first major candidate to jump into in the Buckeye State's 2022 Senate race.

"Today I'm excited to announce that I'm running for U.S. Senate in Ohio," Mandel wrote on Twitter

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Pointing to the on-going impeachment trial of former President Trump, Mandel emphasized that "Watching this sham impeachment has made my blood boil and motivated me to run. I'm going to Washington to fight for President Trump's America First Agenda."

"In Washington, I will pulverize the Uniparty – that cabal of Democrats and Republicans who sound the same and stand for nothing," he vowed. "My candidacy is about standing up for working people, economic freedom and individual liberty. We must stop the far left's assault on American values."

Mandel's the first of what are expected to be many contenders hoping to succeed two-term Republican Sen. Rob Portman, who recently announced that he wouldn't run for re-election next year.

The race in Ohio will likely be one of the most competitive and expensive Senate battles next year, as the GOP tries to win back their majority in the chamber that they lost in the 2020 election cycle.

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In an interview Wednesday with Fox News, Mandel touted that "I’m the most conservative candidate in the race."

And he highlighted his support for the former president, noting that "I was the first statewide official to support President Trump in 2016. I was one of his top fundraisers in Ohio in 2020 and I’m going to Washington to advance the Trump ‘America First’ agenda and to stand up for conservative values."

Mandel said that "I would be honored" to have Trump’s endorsement and support.

Asked by Fox News about his statement earlier in the day that "it’s sickening to see radical liberals and fake Republicans in Washington engage in this second assault on President Donald Trump and the millions of us who supported him," Mandel said one of the "fake Repubicans" is Rep. Anthony Gonzalez of Ohio, who was one of the 10 House Republicans who last month voted to impeach Trump.

Mandel emphasized "I think we need to give fake Republicans like Anthony Gonzalez the boot from the Republican Party"

In this Nov. 4, 2014, file photo, Ohio State Treasurer Josh Mandel speaks at the Ohio Republican Party election night celebration in Columbus, Ohio. (AP Photo/Tony Dejak, File)

Mandel also pledged that "as a United States senator, I’m going to take on squishy Republicans just as much as I’ll take on liberal Democrats. I’m going to Washington to pulverize the uniparty. And the uniparty in my mind is that cabal of Democrats and Republicans who sound the same, stand for nothing, and are more interested in going to cocktail parties than they are in defending the Constitution."

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Mandel's advisers noted to Fox News that the candidate starts the race with $4.5 million cash on hand, left over from his past campaigns.

Responding to Mandel's announcement, the Democratic Senatorial Campaign Committee said that Mandel "represents the very worst of what Ohio voters loathe in politics: a hypocritical, self-serving perennial candidate who always puts himself and his own interests first at their expense."

This is Mandel's third bid for the Senate. Mandel, 43, won the GOP Senate nomination in 2012 but lost in the general election to Democratic Sen. Sherrod Brown. Mandel ran again in 2018 but dropped out of the race citing his wife's health. Mandel and his wife, Ilana Shafran Mandel, divorced in 2020.

Mandel served as Ohio's treasurer from 2011 to 2019.

While Mandel is the first Republican to announce a Senate bid, former Ohio GOP chair Jane Timken is likely to run. She stepped down as chair last week in anticipation of launching a campaign and Fox News has confirmed that she’s staffing up. Rep. Steve Stivers, Ohio Secretary of State Frank LaRose and state Sen. Matt Dolan are all considered potential candidates.

There's speculation that conservative J.D. Vance — the author and venture capitalist known for his memoir "Hillbilly Elegy" — might run.

In the race for the Democratic nomination, longtime Rep. Tim Ryan appears to be moving towards launching a campaign. Former Democratic presidential nominee Hillary Clinton is among the voices calling for Ryan to run.

Rep. Joyce Beatty, Dayton Mayor Nan Whaley, state Rep. Emilia Sykes, and Franklin County Commissioner Kevin Boyce are also considering bids.

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The Senate is split 50-50 between the two parties, but the Democrats control the chamber due to the tie-breaking vote of Vice President Kamala Harris. That means Republicans only have to flip one seat in 2022 to regain the majority they lost following the Democratic sweep in last month’s twin Senate runoff elections in Georgia. But the GOP is defending 20 of the 34 seats up for grabs next year.

Fox News' Mike Emanuel and Caitlin McFall contributed to this report.