Newark Mayor Cory Booker scored a major endorsement Sunday night in his bid to become the next U.S. senator from New Jersey.

George E. Norcross III, the insurance executive and hospital chairman who is seen as the most powerful figure in New Jersey Democratic politics, told The Inquirer that he is endorsing Booker over two congressmen and a top state legislator expected to run in August's primary.

Norcross is a managing partner of the company that owns The Inquirer. His connections to trade labor unions and business leaders means that he can quickly raise money in the unusual, shortened primary campaign and mobilize get-out-the-vote efforts on and before Election Day.

His endorsement also suggests that Democrats across South Jersey, and perhaps through the state, will fall in line and support Booker's candidacy. Under Norcross, the South Jersey Democratic block is often unified, giving it tremendous sway in policy and campaigns.

Norcross is more ideologically aligned with Booker than he is with U.S. Rep. Rush Holt (D., N.J.), who announced his candidacy last week, and U.S. Rep. Frank Pallone (D., N.J.), who plans to announce Monday.

A third formidable candidate, Assembly Speaker Sheila Oliver (D., Essex), told Democratic leaders on Sunday night that she planned to run, a source said.

On the Republican side, Steve Lonegan, a staunch conservative who lost to Gov. Christie in the Republican primary in 2009, is the only established figure so far in the race. Monday at 4 p.m. is the filing deadline for candidates.

Christie himself set this highly unusual, abbreviated campaign into motion last Tuesday, a day after the death of U.S. Sen. Frank Lautenberg, when he announced that instead of a senate election in November 2013 or 2014, there would be special primary on Aug. 13 and a general election on Oct. 16.

In endorsing Booker, Norcross said he saw Booker as his kind of "new Democrat." Specifically, he cited Booker's support for "urban education reform." In 2010 Booker and Christie accepted a $100 million matching grant from Facebook founder Mark Zuckerberg for education reform efforts in Newark, like merit pay for good teachers. And Norcross is in the process of opening several privately-backed public schools in Camden.

"I believe he's a winner," Norcross said of Booker. "And he's representative of a new Democrat — a Democrat that's fiscally conservative yet socially progressive. He's a fighter and not afraid of taking on a tough battle."

Norcross said that he hopes education reform will be a "priority" of Booker's in the senate.

Holt and Pallone are traditional liberals with long-held support from public worker and teacher unions, while Norcross and Booker drew public unions' ire in 2011 when they backed Christie's plan to cut health and pension benefits for teachers and government workers.

After the teachers' union attacked Norcross in a TV ad during that fight, Booker defended him at a news conference.