By ALLISON PECORIN, TRISH TURNER and KENDALL KARSON, ABC News

(WASHINGTON) — In an unexpected move, a top Senate Republican, Missouri Sen. Roy Blunt, announced Monday that he will not run for reelection in 2022.

Blunt, 71, has served in the Senate since 2011 and in the House of Representatives previously.

He’s currently the No. 4 Republican in the Senate.

Blunt announced his plans in a two-minute video released Monday morning.

“After 14 general llection victories — three to county office, seven to the United States House of Representatives, and four statewide elections — I won’t be a candidate for reelection to the United States Senate next year,” Blunt said in the video.

He didn’t explicitly explain why he’s chosen not to run again.

Blunt joins a growing list of veteran Republican incumbents who have announced they will not return the Senate in 2022. He joins Sens. Richard Shelby, R-Ala., Rob Portman, R-Ohio, Pat Toomey, R-Pa., and Richard Burr, R-NC. who have all said they will not seek to keep their seats.

Taken together, the chamber will lose some of its most experienced Republicans next election cycle. Other incumbents up for reelection in 2022 are also being closely watched.

Sen. Ron Johnson, R-Wisc., has not yet announced whether he’ll run to defend his vulnerable seat. And 86-year-old Sen. Chuck Grassley, R-Iowa, also has yet to announce if he’ll seek another term.

Blunt’s planned departure comes as a surprise to many. In late January, Blunt told Politico he was still planning to announce a campaign.

“I’m still planning to run. But that will become official when I announce a campaign. And I’m not doing that yet,” Blunt said. “I really have not been thinking much about it to tell you the truth. … I keep thinking there will be a little breathing space, so far it’s not happening.”

As the top Republican on the Senate Rules Committee and the Joint Congressional Committee on Inaugural ceremonies, Blunt had a busy start to 2021. He coordinated an Inauguration Day with heightened security concerns following the Jan. 6 attack on the Capitol. In the weeks since, the Rules Committee has held multiple hearings examining Capitol security.

Blunt’s exit from decades in politics is likely to set up a scramble for the soon-to-be open seat.

Among the Republicans considering a potential bid is Missouri’s once-embattled Gov. Eric Greitens, who resigned in 2018 amid allegations of sexual misconduct.

“I am evaluating right now what I’m going to be doing this year,” Greitens told a local radio show on a possible political comeback in 2022, before he criticized Blunt for not more forcefully defending former President Trump.

Some of the other Republican state leaders speculated to be potentially eying a run are Attorney General Eric Schmitt, Secretary of State Jay Ashcroft and Lt. Gov. Mike Kehoe.

On the Democratic side, Scott Sifton, a former state senator, and Timothy Shepard, an entrepreneur based near Kansas City, are currently competing for the nomination.

Meanwhile, Jason Kander, Blunt’s 2016 Democratic rival who came within 78,000 votes that year, already took himself out of consideration.

“Regarding the Senate in ’22: Always nice to be asked. Thanks,” he wrote on Twitter. “My decision not to run was never about who I’d run against…I’ll campaign for the Dem nominee!”

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