Democratic officials were overwhelmed by the mayor's popularity and potential, and by visions of him as a campaign heavyweight who could help local candidates for years - and even in November.
"He became a household name in New Jersey, and that's how he established his political credentials with the established political leaders," said State Sen. Ray Lesniak, a longtime power broker from Union County.
"He became a celebrity, he became a folk hero," Lesniak said. "His enormous popularity transcends any personal connection that other candidates have."
Lesniak, who has not made an endorsement, raved about the Booker mythology: famous friends like Oprah Winfrey, a prominent role campaigning for President Obama, his dash into a burning building to save a woman, and his Twitter legions - 1.4 million and counting.
A veteran dealmaker with a taste for French wine, Lesniak said, "Cory Booker has the je né sais quoi that no other New Jersey Democrat has."
South Jersey's top Democrats all have endorsed Booker, as has the party establishment in four North Jersey counties, including the state's three most populous. The support could give Booker an organizational lift as he tries to reach voters for an Aug. 13 primary.
Booker didn't always have such backing.
When the 32-year-old city councilman was trying to make his first big political leap - running for mayor in 2002 - Lesniak and nearly all the state's Democratic leaders backed incumbent Sharpe James. Booker had an outsize following, but James had years of accumulated power, and the establishment helped him defeat the precocious challenger.
But the campaign was featured in a hit documentary, Street Fight, helping propel Booker into a stratosphere few politicians ever reach.
His profile has only risen since.
Booker's national renown will give him instant clout in the Senate, predicted Joe DiVincenzo, a political force and the top elected official in Booker's home county, Essex.
"As soon as he goes in there, he's going to be in the top 10" of the 100 senators, said DiVincenzo, a one-time James supporter who now backs Booker.
South Jersey Democrats see Booker as the leading man, whose guest appearances and fund-raising could be a crucial asset as they contend with Republican Gov. Christie's muscle.
"The mayor will ... give us the greatest opportunity in November in years to come," said Assembly Majority Leader Lou Greenwald (D., Camden).
The irony, Lesniak said, is that Booker's work beyond the state's political circuit built him up, even as local leaders groused that he didn't help enough at home.
"They see the poll numbers," said Lesniak, "and they see him hanging out with the celebrities and the business leaders and the president, and all of that was because of the work he did outside of Newark."
In choosing Booker, 44, party figures have bypassed Reps. Frank Pallone and Rush Holt and Assembly Speaker Sheila Oliver. All three are over 60 and have spent years in the legislative trenches waiting their turns.
"In many respects, I both admire him and am jealous of him," Lesniak said of Booker. "That's life. ... Cory went out and he did this and he established his brand."
Said DiVincenzo: "Everybody wants to be with a winner."
Booker's route isn't an entirely new phenomenon, though in the age of Twitter, viral news, and a fascination with celebrity, it may become more common.
Obama raced to the White House after just a partial Senate term, with the benefit of charisma, inspiring oratory, and friends like Jay-Z and Bruce Springsteen.
Freshmen Republican Sens. Rand Paul and Ted Cruz have been tipped as 2016 contenders, thanks not to bills passed but to fiery speeches and captivating moments, notably Paul's 13-hour filibuster that inspired the Twitter hashtag #StandWithRand.
Critics say Booker's name is far stronger than his resumé, and opponents argue that the odd August primary, with low turnout expected, will be won with grassroots support, not party brawn.
Booker said that his endorsements stemmed from his record in Newark and that he has long helped other Democrats. And if he wins, he has vowed to use his larger platform to aid his allies.
"When you are a statewide elected official," Booker said, "there should be an expectation you have something to prove, that you're going to be there for the whole party, all over the state."
Recently, he recorded a robo-call to help Lesniak in a primary fight. But Lesniak and other admirers said Booker still had a long way to go in building party ties.
"He's got to do a better job with that," DiVincenzo said. "People feel that he's not connected the way he should be connected."
In that way, Booker reminds Lesniak of former New Jersey Sen. Bill Bradley. The Rhodes scholar (like Booker) and NBA champion with the New York Knicks was never close with party insiders. But he had his own fame and success.
Booker, Lesniak said, "took the Bill Bradley route."
So perhaps it's fitting that the two are close. Bradley was one of Booker's closest allies when the rest of the party sided with James. And when Booker announced his Senate run, Bradley again stood at his side.
Only, this time, so did the establishment.
Contact Jonathan Tamari at firstname.lastname@example.org. Follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.inquirer.com/capitolinq.