TRENTON, N.J. — Eight months before any votes are cast, a big winner emerged Thursday in the Democratic primary to replace Gov. Chris Christie.

Senate President Steve Sweeney’s announcement that he won’t seek the nomination in 2017 set a nearly clear field for former Goldman Sachs executive and Obama administration ambassador Phil Murphy.

“It is no secret that I seriously considered running and I believe I would have been able to win the general election and return the governor’s mansion to Democratic control,” Sweeney said in a statement. “However, in the last few days it has become clear that Phil Murphy has been able to secure substantial support from Democratic and community leaders that would make my bid all but impossible.”

Murphy is a wealthy businessman who retired from the Wall Street firm after 23 years. He served as ambassador to Germany under President Barack Obama from 2009 to 2013.

Brigid Harrison, a professor of political science at Montclair State University, said Sweeney’s move “unofficially anoints Murphy as the next governor. “None of the other potential candidates, either Democratic or Republican, has the ability to match the millions of dollars that Murphy is willing to spend to become governor.”

Sweeney’s announcement came before Democratic chairs of the voter-rich Bergen, Passaic, and Hudson counties endorsed Murphy at a news conference Thursday afternoon. It also came a week after Jersey City Mayor Steve Fulop said he wouldn’t run for governor as he was expected to and would instead support Murphy. That outsized support from the more populous northern part of the state would make it difficult for Sweeney — who has strong ties to southern New Jersey — to win in June.

Sweeney, a West Deptford resident and vice president of the International Association of Iron Workers, had lined up early support from some unions, including the union representing Atlantic City’s casino workers, United Food and Commercial Workers, and the United Auto Workers.

Sweeney said he eagerly anticipates working with Murphy next year during the campaign. He said he intends to seek re-election for his Senate seat, which he’s held since 2002.

Murphy said Thursday night, “I look forward to a campaign of ideas, a campaign of optimism and hope, a campaign that will set a new course for our people and the state which we all love.”

State Sen. Ray Lesniak of Union County and Assemblyman John Wisniewski of Middlesex County are considering seeking the Democratic nomination for governor. Both this week opposed a deal brokered by Sweeney, Assembly Majority Leader Vincent Prieto and Republican Gov. Chris Christie to raise the gasoline tax by 23 cents a gallon to fund transportation projects while cutting other taxes. The measure is slated for a vote in the Legislature on Friday.

Wisniewski told Thursday that he was planning to set up an exploratory committee to consider his run, while Lesniak said he’d prefer a head-to-head race against Murphy. “It’ll focus the campaign on Goldman Sachs vs. the people,” he said.

Republican Assemblyman Jack Ciatarelli of Somerset County declared his candidacy on Tuesday. Lt. Gov. Kim Guadagno and Assembly Minority Leader Jon Bramnick are other potential candidates for the GOP nomination.

The state constitution bars Christie from seeking a third term, and he’ll leave office in January 2018.

Associated Press writer Wayne Parry in Atlantic City contributed to this story.