John Wisniewski Bernie Sanders

State Assemblyman John Wisniewski (D-Middlesex) cheers for Bernie Sanders at the Democratic National Convention in Philadelphia last year.

(Aristide Economopoulos | NJ Advance Media for NJ.com)

TRENTON -- U.S. Sen. Bernie Sanders announced Friday that he has not endorsed any candidate -- at least not yet -- in New Jersey's governor's race, delivering what some saw as a blow to underdog Democratic contender John Wisniewski, one of Sanders' biggest supporters in the Garden State.

The announcement came a few hours after Wisniewski's top opponent, Democratic front-runner Phil Murphy, trotted out the support of Sanders' son, Levi Sanders.

Both were surprise developments, considering Wisniewski was the New Jersey chairman of Bernie Sanders' 2016 presidential campaign.

But Wisniewki's campaign downplayed the moves, noting that Sanders still praised the candidate, and then announced its own Sanders-related endorsement later in the day -- from Jeff Weaver, the Vermont senator's former presidential campaign manager.

The dizzying cascade of news shed a spotlight Friday on the increasingly heated battle between Wisniewski and Murphy for their party's nomination to succeed Republican Gov. Chris Christie -- and the tug of war for support from progressive voters who flocked to Sanders in 2016.

Wisniewski is a veteran member of the state Assembly who was the only major New Jersey Democrat to support Sanders for president. He is now running a Sanders-like grassroots campaign for governor, painting himself as a political "outsider" despite his 21 years in Trenton.

Experts say it appeared Wisniewski expected an endorsement from Sanders would bolster his chances against Murphy, a millionaire former banking executive at Goldman Sachs and a former U.S. ambassador to Germany. Murphy supported eventual Democratic nominee Hillary Clinton over Sanders in 2016.

But in an email blasted out to Murphy's supporters on Friday morning, Sanders' only biological son -- a 47-year-old Social Security and benefits specialist at a Massachusetts law firm -- said he's been following the governor's race in part because he has cousins who live New Jersey and noted that he recently spoke with Murphy.

"To say I was impressed by his progressive vision would be an understatement," Levi Sanders wrote about Murphy, who has never held elected office. "Like us, Phil is a fighter. He's not part of the system and doesn't owe the special interests anything."

Levi Sanders also announced he will campaign with Murphy in New Jersey on Feb. 11. A location has not yet been determined.

Robert Becker, Wisniewski's campaign manager, called the endorsement "odd," noting that as an ex-banker, Murphy "played a starring role in screwing up our economy."

"John remains committed to the progressive movement that Bernie Sanders led last year, and we look forward to earning his support," Becker told NJ Advance Media.

Shortly thereafter, Bernie Sanders released a statement saying he wanted to thank Wisniewski for "the strong support he gave me" in 2016.

"He played a great role in that race, and I am confident he would make an excellent governor for New Jersey," Sanders added.

But the senator -- who is technically an independent -- noted that the state's Democratic primary is "hotly contested" and "there are those who supported me in 2016 who are supporting John and others who are supporting his opponent."

"For that reason alone, I have not endorsed in the New Jersey governor's race," Sanders concluded.

Becker pointed out that Sanders said Wisniewski would be an "excellent" governor and that he did not rule out making an endorsement in the future.

Then, later Friday afternoon, Wisniewski's campaign announced the endorsement from Weaver.

"We need John Wisniewski's progressive leadership in the New Jersey governor's office, not the failed politics of the establishment or his Goldman Sachs-backed opponent," Sanders' campaign manager said in a statement.

"John Wisniewski joined this movement when we needed him the most," Weaver added. "Now is the time for us to return the favor."

But experts said not getting Sanders' endorsement hurts Wisniewski.

"A Sanders endorsement would be a huge lift to him," said Ben Dworkin, director of the Rebovich Institute for New Jersey Politics at Rider University. "The fact he didn't get it is a huge disappointment -- though it doesn't mean he won't be able to get strong support from those who supported Sanders in 2016."

Brigid Harrison, a political science professor at Montclair State University, said: "While Sanders comments were supportive, they don't serve as a battle cry in the way that an endorsement would have."

Matthew Hale, a political science professor at Seton Hall University, said at a minimum, a Sanders endorsement "would have caused Bernie supporters to at give Wisniewski a second look" -- but it still "wouldn't have been enough for him to overcome Murphy."

Patrick Murray, director of the Monmouth University Polling Institute, agreed.

"Murphy has the organization locked up," Murray said. From Sanders's point of view, there is no upside to backing a horse here."

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.