CINCINNATI (AP) — Ohio Sen. Rob Portman said Monday that he won’t seek reelection to a third term in 2022, expressing dismay with the deep partisanship and dysfunction in American politics.

The career establishment Republican with a reputation for bipartisanship cited a political climate that has made it “harder to break through the partisan gridlock and make progress."

“Our country is very polarized,” Portman said, adding that former President Donald Trump did not help with the polarization. “It’s shirts and skins right now. We need to tone it down.”

The decision is one measure of the difficult politics facing many Republicans in Washington as they cede power in President Joe Biden's administration and watch their party split between hard-right Trump supporters and others eager to turn the page. Portman, a moderate who might see growing influence as Biden looks for allies, did not appear optimistic about the prospect of a new political climate.

Portman, 65, is among the longtime Republican lawmakers who often backed Trump, though not vociferously. Once dubbed “The Loyal Soldier” in a front-page profile story in his hometown Cincinnati Enquirer, Portman usually defended Trump or avoided criticism of him with carefully worded statements. After Trump called the presidential election rigged, citing no legitimate evidence, Portman said Trump had a right to a probe of any irregularities.

But immediately after the Jan. 6 insurrection at the U.S. Capitol by a violent mob of Trump backers, Portman said Trump needed to go on national TV to tell his supporters to refrain from violence.

“Both in his words before the attack on the Capitol and in his actions afterward, President Trump bears some responsibility for what happened,” Portman said.

His retirement adds another open seat for the GOP to defend in 2022 as it seeks to regain control of a Senate that Democrats hold by virtue of Vice President Kamala Harris being the tiebreaking vote. Sens. Richard Burr of North Carolina and Pat Toomey of Pennsylvania, two other more mainstream Republicans in the Senate GOP caucus, have also said they won't seek reelection next year.

“There goes the kind of really thoughtful public official who listens, who works both sides, who tries to get things done,” Republican pollster Christine Matthews said. “And right now the kind of candidate that’s going to come out of a Ohio Republican primary is not going to be that kind of candidate. That’s not the kind of energy that’s in the Republican primary electorate right now.”

Indiana Sen. Todd Young, former chair of the National Republican Senatorial Committee, said he wasn't worried about moderates fleeing the party.

“(Portman's departure) says nothing about the 2022 landscape," Young said. "It says a lot about Rob Portman that, two years out, he made the announcement so that Republicans have plenty of time to field a very strong candidate and to give that candidate sufficient time to run a strong campaign, which they will.”

Eight-term Rep. Jim Jordan, an outspoken Trump supporter from western Ohio, and six-term Rep. Bill Johnson, from heavily pro-Trump southeast Ohio, are viewed as potential candidates for Portman's seat. Likewise, former Rep. Jim Renacci from central Ohio, a Republican who lost a Senate challenge to Democrat Sherrod Brown in 2018, is also considered a possible contender.

Portman’s announcement came the same day that the Senate is receiving the House impeachment article against Trump for his role in the Capitol riot. While some Republican senators have criticized going ahead with the trial with Trump out of office, Portman said last week that he would listen to the evidence presented by both sides before deciding how to vote.

Republicans have 20 seats up for reelection in 2022, compared to 14 for Democrats. Those GOP seats include presidential battlegrounds Wisconsin, where Trump narrowly lost in November, and Florida, where he won by more than 3 percentage points.

Wisconsin Sen. Ron Johnson has not yet said whether he'll seek a third term. Meanwhile, six-term Iowa Sen. Chuck Grassley, who would turn 89 two months before the 2022 election, said he would decide this year whether to seek a seventh. Two-term Missouri Republican Roy Blunt has not said whether he'll seek a third.

Ohio, a perennial battleground for decades, has become more reliably Republican, carried by Trump by more than 8 percentage points in 2016 and 2020. Portman, like many mainstream GOP lawmakers viewed as insufficiently supportive of Trump, was considered likely to face a primary challenge from the right.

“Yeah, sure, some people are mad at him,” said Ohio Republican strategist Ryan Stubenrauch. “But he wouldn't have faced a credible primary challenge. He does his job. He's a really good campaigner and well known across the state.”

Portman twice won election to the Senate by wide margins. Before that, he served seven terms in the House and a stint as President George W. Bush's budget director.

Still, Portman's departure offers a glimmer of hope for Democrats in the state. Besides Democratic Sen. Sherrod Brown, most other statewide officials are Republican.

Tim Ryan, a 10-term Democratic representative from blue-collar eastern Ohio who ran unsuccessfully for the 2020 presidential nomination, said Monday that he is weighing a Senate campaign. “I haven’t made a decision yet but I’m looking seriously at it," he wrote on Twitter.

Likewise, Dayton Mayor Nan Whaley, a rising star who lost a 2018 primary for governor, said she is weighing a Senate bid. “I've gotten a lot of encouragement, especially today, and will make my decision in the coming weeks,” Whaley told The Associated Press.

Portman’s first federal government job started in 1989, when he served as an associate legal counsel in the George H.W. Bush White House. Portman considered Bush a mentor, one whose genteel style was far from that of the abrasive Trump and some of his Republican supporters in Washington

Portman was elected to Congress from southern Ohio in a 1993 special election and won six more elections before President George W. Bush tapped him to serve as U.S. trade representative in 2005. He traveled the globe, negotiating dozens of trade agreements. Bush then nominated him to be White House budget director in 2006.

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Beaumont reported from Des Moines, Iowa.

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Follow Dan Sewell at https://twitter.com/dansewell