Republican gubernatorial candidate Doug Mastriano at primary election night party on May 17, 2022 in Chambersburg, Pennsylvania.
CNN  — 

Pennsylvania state Sen. Doug Mastriano, a fervent election denier who lost last year’s gubernatorial race, said he’s not running for US Senate on Thursday night, a relief for some Republicans who had feared the controversial conservative would complicate their hopes of flipping a Democratic-held seat.

“At this time, we have decided not to run for the US Senate but to continue to serve in Harrisburg,” he said on Facebook Live.

Mastriano appeared to leave himself some wiggle room, going on to repeat, “At this time, at this moment, the way things currently are, I am not running for the US Senate seat.” But he said he’d support the eventual nominee.

Mastriano, who had lost the governor’s race by 15 points six months ago, had come under pressure to stay out of the race from some Pennsylvania and national Republicans, who were concerned he’d be too extreme to win a general election against Democratic Sen. Bob Casey, who’s running for a fourth term.

“Your appearance at the top of the Republican ticket last year undoubtedly contributed to Republicans losing the majority in the PA House, and I fear a repeat of that in 2024,” Republican state Rep. Russ Diamond had written this week in an Op-Ed titled, “Let’s encourage Doug Mastriano to sit this one out,” published on a conservative news website based in Philly.

National Republicans, who need a net gain of one or two seats to flip the Senate next fall depending on which party wins the White House, have their eyes on former hedge fund executive Dave McCormick. The wealthy Republican lost the GOP Senate nomination last year to Mehmet Oz, who went on to lose the general election to now-Sen. John Fetterman. McCormick, who has yet to announce a Senate campaign, responded to Mastriano’s announcement in a statement Thursday saying he’s “seriously considering a run.”

Senate Minority Leader Mitch McConnell has called McCormick a “high-quality candidate.” Asked earlier this spring if he was concerned about a potential Mastriano bid, the GOP leader told CNN’s Manu Raju, “I think everybody is entitled to run. I’m confident the vast majority of people who met Dave McCormick are going to be fine with him.”

Running with former President Donald Trump’s endorsement last fall, Mastriano lost to Democratic now-Gov. Josh Shapiro. His far-right positions on issues like the 2020 presidential election and abortion had created anxiety among some Republicans that he could once again alienate swing-county voters in Pennsylvania, which is No. 8 on CNN’s ranking of the Senate seats most likely to flip in 2024.

Prominent election denier

Mastriano, a retired Army colonel who has served in the state Senate since 2019, rose to national prominence as an election denier who attempted to overturn voters’ will in 2020.

In an interview with CNN earlier this spring, Mastriano acknowledged his loss to Shapiro last year but still refused to acknowledge that President Joe Biden beat Trump in 2020.

His state Senate campaign had chartered buses to Trump’s Washington, DC, rally on January 6, 2021, and Mastriano himself was pictured on the US Capitol grounds that day. He was questioned by the FBI and handed over some documents to the House select committee probing January 6 in response to a subpoena, but has not been charged with any wrongdoing.

Trump endorsed Mastriano days before the GOP gubernatorial primary in 2022, and he finished solidly on top of a crowded Republican field.

But Mastriano did not run a conventional general election campaign. He declined interviews with several local media outlets, relied on Facebook and social media for voter interaction, and was outspent by tens of millions of dollars in advertising by his opponents.

This story has been updated with additional information.

CNN’s Simone Pathe and Kit Maher contributed to this report.