U.S. Sen. Rob Portman (R-Ohio) on Monday announced that he will not seek re-election in 2022 and will retire from the Senate at the end of his current term.

Portman, 65, will publicly announce his decision at a press conference at the Hilton Netherland Plaza in downtown Cincinnati, the Cincinnati Enquirer reported.

"This was not an easy decision because representing the people of Ohio has been an honor," Portman said in a statement. "But I've been doing this a long time, longer than I ever intended."

Speaking to the Enquirer, Portman explained that "partisan gridlock" has made it difficult to accomplish much in the Senate and has contributed to his decision to leave Washington after working more than 30 years in various public service positions.

"I don't think any Senate office has been more successful in getting things done, but honestly, it has gotten harder and harder to break through the partisan gridlock and make progress on substantive policy, and that has contributed to my decision," Portman said.

"During my service in the Senate, I am proud of what we've been able to accomplish for Ohio and the country. I have consistently been named one of most bipartisan Senators. I am proud of that and I will continue to reach out to my colleagues on both sides of the aisle to find common ground," he added.

Portman was first elected to the Senate in 2010, going on to serve for two terms. Prior to that, he served as a U.S. representative from Ohio's 2nd Congressional District for seven terms, from 1993 to 2005. His first job in Washington was in 1989, serving as a legislative aide to President George H.W. Bush. In 2005, Portman left Congress to work in the White House for President George W. Bush as the U.S. trade representative. In 2006 he was promoted to direct the Office of Management and Budget for Bush.

His retirement presents Democrats with an opportunity to expand their Senate majority in 2022, an election year that is already seen as challenging for Republicans. There are 14 Democrats and 20 Republicans who will be up for re-election in two years. Three of those Republicans, including Portman, have already announced they will retire from the Senate. The other two retiring senators are Pat Toomey (R-Pa.) and Richard Burr (R-N.C.).

Democrats hold the narrowest of Senate majorities, relying on Vice President Kamala Harris to break 50-50 ties in their favor. If their incumbents win re-election, they need to win just one Republican-held seat to claim the majority outright.

Portman's retirement is also likely to trigger an intense Republican primary battle for the nomination for Senate. Speculative candidates mentioned by the Enquirer include Rep. Jim Jordan, Ohio Republican Party Chairwoman Jane Timken, former state Treasurer Josh Mandel, and "Hillbilly Elegy" author J.D. Vance.