The expulsion of George Santos from Congress on Friday swept away one major political headache for Republicans, but it immediately set the stage for another: The party will have to defend his vulnerable seat in a special election early next year.The race in New York is expected to be one of the most high-profile and expensive off-year House contests in decades. It has the potential to further shrink Republicans’ paper-thin majority and offer a preview of the broader battle for House control next November.With towering stakes, both parties have been preparing for the possibility for months, as Mr. Santos’s fabricated biography unraveled and federal criminal charges piled up. More than two dozen candidates have already expressed interest in running, and labor unions, super PACs and other groups have begun earmarking millions of dollars for TV ads.“It’s going to be like a presidential election for Congress,” said Steve Israel, a Long Island Democrat who once led his party’s House campaign arm. “It becomes ground zero of American politics.”Gov. Kathy Hochul of New York has 10 days to formally schedule the contest after Friday’s lopsided vote to remove Mr. Santos. But both parties expect the election to take place in mid-to-late February, just over a year after he first took the oath of office.Unlike in a normal election, party leaders in Washington and New York — not primary voters — will choose the Democratic and Republican nominees. They were moving quickly to winnow the field of potential candidates, and could announce their picks in a matter of days.George Santos Lost His Job. The Lies, Charges and Questions Remaining.George Santos, who was expelled from Congress, has told so many stories they can be hard to keep straight. We cataloged them, including major questions about his personal finances and his campaign fund-raising and spending.Democrats were expected to coalesce around Thomas R. Suozzi, a tested centrist who held the seat for six years before Mr. Santos but gave it up for a failed run for governor in 2022. Mr. Suozzi, 61, is a prolific fund-raiser and perhaps the best-known candidate either party could put forward. Anna Kaplan, a former state senator, is also running and has positioned herself to Mr. Suozzi’s left.The Republican field appeared to be more fluid. Party leaders said they planned to interview roughly 15 candidates, though officials privy to the process said they were circling two top contenders, both relative newcomers: Mike Sapraicone, a retired New York Police Department detective, and Mazi Pilip, an Ethiopian-born former member of the Israel Defense Forces.Political analysts rate the district, stretching from the outskirts of New York City into the heart of Nassau County’s affluent suburbs on Long Island, as a tossup. President Biden won the district by eight points in 2020, but it has shifted rightward in three consecutive elections since, as voters fearful about crime and inflation have flocked to Republicans.Democratic strategists said they would continue to use the embarrassment of Mr. Santos to attack Republicans, blaming them for aiding the former congressman’s rise. But recapturing the seat may be more difficult than many Democrats once hoped.Local Republicans moved decisively to distance themselves from Mr. Santos last January, and the strategy has shown signs of working. When Long Island voters went to the polls for local contests last month, they delivered a Republican rout that left Democrats scrambling to figure out how to rehabilitate a tarnished political brand.“Anyone who thinks a special election on Long Island is a slam dunk for Democrats has been living under a rock for the last three years,” said Isaac Goldberg, a strategist who advised the losing Democratic campaign against Mr. Santos in 2022.“Politics is a pendulum,” he added. “Right now, it’s on one side, and it’s unclear when it’s going to swing back.”Republicans face their own challenges, though, particularly in an idiosyncratic contest likely to favor the party that can turn out more voters. Democratic voters in the district have spent months bemoaning their ties to Mr. Santos and are highly motivated to elect an alternative. It is unclear if Republican supporters will feel the same urgency their leaders do.“It’s been a frustrating year,” said Joseph Cairo, the G.O.P. party chairman in Nassau County. “I look at this as just the beginning to right a mistake, to move forward, to elect a Republican to serve the people the proper way, to elect somebody who is for real — not make believe.”The outcome promises to have far-reaching implications for the current Congress and the next.After Mr. Santos’s ouster, Republicans have a razor-thin majority. Thinning it further could hamper their short-term ambitions to pursue an impeachment inquiry into President Biden and negotiate around a major military aid package for Israel.Whoever emerges as the winner in February would also likely become the front-runner for next fall’s elections and lend their party momentum as they prepare to fight over six crucial swing seats in New York alone, including a total of three on Long Island.Democrats believe Mr. Suozzi, who is currently working as a lobbyist, is best positioned to deliver. In his stints as a congressman and Nassau County executive, he took conservative stances on public safety and affordability that are popular among suburban voters. And his combative primary campaign for governor just last year may help him shake the anti-Democratic sentiment that has sunk other candidates.Jay Jacobs, the Democratic leader for the state and Nassau County, said he still intended to screen multiple candidates, including Ms. Kaplan, a more progressive former state senator who remains in the race, even as other candidates dropped out and coalesced behind Mr. Suozzi.Ms. Kaplan could get a boost from Ms. Hochul, who faced Mr. Suozzi in an ugly 2022 primary fight, during which he questioned her husband’s ethics and referred to her as an unqualified “interim governor.”The governor has pushed Mr. Jacobs and Representative Hakeem Jeffries of New York, the House Democratic leader, to reconsider whether Mr. Suozzi was their strongest candidate, particularly given his hesitancy to fully embrace abortion rights in the past, according to four people familiar with the conversations.But it is unclear if the governor would have the power to block Mr. Suozzi. Mr. Jeffries personally worked to lure the former congressman into the race earlier this fall, and Mr. Suozzi is close friends with Mr. Jacobs, who has told associates he is the likely pick.Republicans are proceeding more cautiously. They are wary of repeating their experience with Mr. Santos, who secured the party’s backing in 2020 and 2022 despite presenting them with a fraudulent résumé and other glaring fabrications that they failed to catch.This time, Republicans appear to only be considering candidates already known to party officials, and plan to engage a research firm to more formally vet potential nominees.Campaign strategists in Washington were said to favor Mr. Sapraicone, the former police detective who made a small fortune as the head of a private security company. Mr. Sapraicone, 67, could afford to spend a portion of it in a campaign, but he would also enter a race with almost no name recognition or electoral experience.Local Republicans were pushing Ms. Pilip, a potentially mold-breaking rising star with a remarkable biography. She moved to Israel from Ethiopia as a refugee in the 1990s, later served in the Israel Defense Forces and flipped a legislative seat in Nassau County in her 40s as a mother of seven.Other wild card candidates included Elaine Phillips, the Nassau County comptroller; Kellen Curry, an Air Force veteran and former banker; and Jack Martins, a well-known state senator who has run for the seat before.Mr. Santos himself could theoretically run for the seat as an independent. But the task would be arduous and might jeopardize a more urgent priority: fighting charges that could put him in prison for up to 22 years. More