Booker announced his candidacy Saturday at stops in Newark and Willingboro, becoming the biggest name in a race Democrats have flocked to, sensing opportunity, while most Republicans have shied away.
Most analysts see Booker as the favorite, but stumbling blocks remain, particularly with two potential opponents - Democratic Congressmen Frank Pallone and Rush Holt - who have deep ties to the labor unions and left-leaning groups that are particularly powerful in primary elections.
Both have long coveted a Senate seat, and a short 2013 race helps them. First, a run in 2014 would have forced them to give up their House seats. Now, they get a risk-free shot at an open seat, a rare prize. And second, Booker now has less time to build on his broad fund-raising network, which stretches from New York City to Hollywood. (Facebook founder Mark Zuckerberg is among those ready to jump in to raise money for him.)
The contest, though, begins with Pallone ahead of Booker in the money department: $3.7 million to $1.6 million. Pallone also benefits from his grassroots appeal and longtime party loyalty. Having worked the local Democratic circuit over 13 terms in office and built bonds with party king-makers, he might fare better in an odd August primary if hard-core Democrats dominate the turnout.
But as Pallone and Holt, the dark-horse candidate, scramble for the Senate, the congressmen who have cast themselves as the liberal heirs to Lautenberg could split votes.
"The true-believer liberals now have two candidates to pick from," said Monmouth University political scientist Patrick Murray.
One Democratic insider described the race as Booker against "Rush Pallone."
Booker, despite his challenges, still has by far the highest favorability and name recognition in the race: 55 percent of registered voters saw him favorably in a February Monmouth poll, and 72 percent didn't know enough about Pallone to form an opinion, leaving him much ground to make up in a short time. Cable channels broke into their shows Saturday to cover Booker's campaign announcement.
In stark contrast to the congressmen, the mayor has promoted himself as a post-partisan problem-solver who would reach across the aisle in Washington.
"I will be relentless in my pursuit of common ground, unyielding in my effort to bring people together, and choosing pragmatism over partisanship," he said in Newark on Saturday.
Liberal critics, however, could also wield his bipartisan friendship with Christie against him.
Booker's strong approval ratings will be tested as opponents dig into his record and see how he takes a punch. Newark still has a major crime problem, and some politicians in the city deride him for spending too much time out of state building his brand.
The winner of the Democratic primary, analysts and several insiders of both parties say, will be the heavy favorite to win the Senate seat. Even Republicans say privately that many potential GOP candidates don't have the muscle to collect 1,000 signatures by Monday, the filing deadline, or go raise enough money in just a few months.
Christie's reelection campaign is drawing much of the state's Republican resources and cash, and history is working against the party: New Jersey hasn't elected a Republican senator in 40 years.
The state's well-known Republicans have backed away from the race, underscoring the extent to which New Jersey's GOP is a one-man Christie show.
"We're hearing crickets from Republicans right now," Murray said.
But the dearth of candidates, and an interim senator, Jeff Chiesa, who won't run, means opportunity for Steve Lonegan, the first Republican to declare his candidacy.
The former head of the New Jersey chapter of the Koch brothers-affiliated Americans for Prosperity, Lonegan has made his name as a conservative firebrand - a rare breed in blue New Jersey. In two gubernatorial primaries he has lost out to more centrist candidates but may now have a clear path to a statewide nomination.
"I'm the best candidate to go into the Senate and make Harry Reid's life miserable," Lonegan, 57 said in an interview, referring to the Senate's Democratic leader. "The Obama administration policies are hurting our country's future, liberty, and economic prosperity."
If Lonegan won the party's nomination, his bomb-throwing style could make life difficult for Christie and Republican lawmakers, who are all on the ballot in November and have built more moderate profiles.
But his nomination also would liberate local Republican organizations: Because Lonegan is outside the establishment, they wouldn't be obligated to provide him money or muscle on the ground.
By Monday, when petitions are due, at least the field will settle. One huge wild card will remain: timing.
Will voters, who just last week went to the polls for one primary, and who will be bombarded with ads for the November gubernatorial election, come out for August and October voting dates, too? Who will leave the beach to vote in the heat of summer?
"There's no precedent for this situation," Murray said.
One veteran operative predicted that county machines, usually the driving forces for turnout, will hardly invest in the Senate race, since county and state-level candidates won't be on the ballot in August or October. The Senate hopefuls themselves will have to draw voters to the polls.
"This is really, really going to come down to who has the best field operation," the operative said.
"For all of you who were bored with the governor's race," Christie said Tuesday, "I have now solved your problem."
The scramble, with well-established names consuming airtime and resources, threatens to drown out the Democratic gubernatorial candidate, State Sen. Barbara Buono - one perhaps predictable outcome that might suit Christie just fine.
Contact Jonathan Tamari
at firstname.lastname@example.org or follow on Twitter @JonathanTamari. Read his blog, "Capitol Inq," at www.inquirer.com/CapitolInq.