FILE - In this Nov. 2, 2020 file photo, Rep. Conor Lamb, D-Pa., speaks during a rally for Democratic presidential candidate former Vice President Joe Biden at Community College of Beaver County, in Monaca, Pa. Lamb's district may all but disappear or, at the very least, become more hostile in redistricting before the next election. Meanwhile, he has said he will consider running for Pennsylvania's open U.S. Senate seat in 2022.

U.S. Rep. Conor Lamb, D-17th, said Friday he is running for Pennsylvania's open Senate seat, joining a crowded Democratic field in one of the nation's most competitive races.

Lamb is seeking the nomination to replace outgoing GOP Sen. Pat Toomey. Lamb, a former Marine and federal prosecutor, rose to political prominence three years ago when he beat a Donald Trump-backed Republican in a special election that foreshadowed the 2018 Democratic takeover of the House.

The Senate race is wide open on both sides and is expected to be among the most expensive in a 2022 U.S. midterm election that will decide party control of an evenly split Senate. Toomey is retiring after two terms.

Lamb said in a YouTube video posted Friday that he is running, declaring: "I believe this is the most important Senate seat in the country."

He planned to launch his campaign Friday afternoon at a union hall in Pittsburgh before heading out on a statewide tour.

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