U.S. Rep. Chrissy Houlahan won’t run for Pennsylvania’s open U.S. Senate seat next year and will instead seek reelection in her Chester County-based congressional district, she said Tuesday, further shaping the contours of a critical Senate primary.

The decision, disclosed first in a statement to The Inquirer, removes a much-watched Democratic figure, and potentially strong contender, from a Senate race that could determine control of the chamber.

Houlahan, an Air Force veteran and prolific fund-raiser from the state’s most populous region, was openly considering a run and widely seen as a possible favorite for moderate Democrats hoping for an alternative to some of the more liberal candidates in the race.

With Houlahan exiting the fray, even more attention is likely to turn to U.S. Rep. Conor Lamb, an Allegheny County Democrat who is also considering a Senate run and comes from the party’s more moderate wing. While many liberals are seeking a bold, progressive voice to represent the party, other Democrats are hoping for a nominee who fits the mold of President Joe Biden and Democratic Sen. Bob Casey, pointing to their successes in the state.

Houlahan said her “highest best use” is to remain in the House, where Democrats are defending a narrow majority and face a difficult task to retain control in next year’s midterm elections.

“I came to Washington to serve my community, Commonwealth and country at what I believe to be an existential inflection point for our nation,” Houlahan said. “Over the past few months, I have considered whether that ‘highest best use’ should translate to a run for Senate. I have decided that my purpose in service at this time remains as the Congresswoman for the great people of Pennsylvania’s sixth Congressional district.”

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With Republican Sen. Pat Toomey declining to seek reelection next year, Pennsylvania’s Senate race is expected to be among the most competitive in the country, and one of a handful that could decide which party has the majority. At stake are Biden’s policy agenda and ability to advance nominees in the second half of his term. Democrats see Pennsylvania as one of their best opportunities to gain a seat in the chamber, which is currently split 50-50, with Democrats in control only because of Vice President Kamala Harris’ ability to cast tie-breaking votes.

Houlahan’s House district, though, could also present a challenge for her party. After once leaning Republican, it has shifted leftward as suburbs nationwide have moved toward Democrats and is now relatively safe for an established incumbent. But Houlahan and fellow Democrats worry it could become more competitive when district lines are redrawn next year after the decennial census — and in the face of what could be a GOP wave in 2022, since the party in power in Washington historically loses seats in midterm elections.

“As we look towards redistricting and the 2022 races, it is crucial not only that Democrats retain control of the House but that we also succeed in expanding our majority in the Senate,” said Houlahan, first elected in 2018 as part of a political wave driven by Democratic women. “I will do everything I can to make sure Pennsylvania proudly sends two Democrats to the Senate.”

Houlahan, with $3.5 million in her campaign account, had openly mulled a Senate run, but for weeks Democratic insiders had quietly questioned whether she would make the leap.

Her decision leaves Lt. Gov. John Fetterman, State Rep. Malcolm Kenyatta of Philadelphia, and Montgomery County Commissioner Val Arkoosh as the most prominent Democrats in the Senate field.

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It also leaves Arkoosh, for now, as the only woman in the race and the only one from the Philadelphia suburbs, which have become a key piece of the Democratic coalition. EMILY’s List, a national group that aids Democratic women who support abortion rights, is closely watching the contest in a state that has never elected a woman to the Senate. But with multiple women considering a run, it hasn’t jumped in.

Houlahan’s departure narrows the options, though U.S. Rep. Madeleine Dean, of Montgomery County is still considering a bid. Should Dean run, her profile could draw some of the same suburban voters that Houlahan may have reached — though she and Arkoosh, from the same county, might also carry similar appeals.

State Sen. Sharif Street, of Philadelphia, is also considering a Senate campaign.

On the Republican side, former congressional candidate Sean Parnell, real estate developer Jeff Bartos, former congressional candidate Kathy Barnette, attorney Sean Gale, and private intelligence firm founder Everett Stern are among those campaigning for the seat.