TRENTON — Gov. Christie on Thursday called the Democratic front-runner in the race to succeed him a "fraud," declaring Phil Murphy's decision to limit campaign spending "meaningless" because dark money groups would try to rescue his candidacy if the general-election campaign became competitive.

Speaking during a news conference on an unrelated topic, Christie, a Republican, also compared Murphy to his predecessor as governor, Jon S. Corzine, a Democrat who was CEO of the Wall Street firm Goldman Sachs for part of the time Murphy worked there.

"The only difference between Phil Murphy and Jon Corzine is Phil Murphy doesn't have a beard," Christie said. "They both bought the nomination," he said, though "at least Corzine had some experience in government" as a U.S. senator.

Phil Murphy, the Democratic front-runner
Mel Evans
Phil Murphy, the Democratic front-runner

Christie's remarks came a day after Murphy's campaign said he would participate in the state's public-financing program should he win Tuesday's Democratic primary. Murphy, a former ambassador to Germany who has not held elective office, has spent $20 million on the campaign and invested $16 million of his own money.

He leads the Democratic field with triple the support of any other candidate, according to the most recent poll. In a hypothetical general-election match-up with Republican front-runner Lt. Gov. Kim Guadagno, Murphy leads, 50 percent to 25 percent, according to a May 3 Quinnipiac University survey.

"If that gets to single digits, you and I can have whatever bet you want to have about whether a third-party group with anonymous donors will show up with tens of millions of dollars with attack ads against Guadango or [Assemblyman Jack] Ciattarelli," Christie told reporters.

"We won't be able to trace that money until it's long over, if ever. But I guarantee you it's coming from Phil and Tammy Murphy," Christie said, referring to Murphy's wife.

In a statement, Murphy adviser Julie Roginsky said, "The last person who should be giving anyone advice on ethics in government is Chris Christie, who is apparently too toxic even for Donald Trump to touch."

Murphy's opponents have accused him of hypocrisy, saying he ignored their calls to limit spending in the primary, and have long argued that he has tried to buy the Democratic nomination by donating to influential county party chairs and committees.

His top rivals are former U.S. Treasury Undersecretary Jim Johnson, Assemblyman John S. Wisniewski, and State Sen. Raymond J. Lesniak.

Murphy says he has cut checks and traveled the state to help build the party. Christie, who defeated Corzine in 2009, is term-limited and will leave office in January.

"If there were limits on spending, Phil Murphy wouldn't be a serious candidate for governor," Christie said. "He became a serious candidate for governor because he wrote checks to every man, woman, and child who mattered in the Democratic Party to buy their support. Come on. What in his background makes him a serious candidate for governor of New Jersey?

"I don't know, because he was ambassador to Germany? Is he appealing to our particularly large German American community in New Jersey?" Christie said. "I don't know."

Under the public-financing program, candidates cannot spend more than $13.8 million in the general-election campaign. Murphy's commitment to that limit would be meaningful only if he promised to disavow spending by third-party groups on his behalf, Christie said.

Christie has received support from outside groups in his campaigns.

After he dropped out of last year's presidential race, Christie was a top supporter of Trump, who had no experience in government before he won the White House. A number of Trump's advisers are, like Murphy and Corzine, former Goldman executives.

The governor predicted that if New Jersey returned to "Goldman Sachs politics" in November, Republicans would retake the governor's mansion in 2021.

Christie is staying neutral in the Republican primary, saying that as head of the party he does not want to tilt the race. But he said he would endorse the GOP nominee.

Despite his harsh words for Murphy, Christie said he had "great admiration for everybody in this race" except for "the knucklehead" Bill Brennan, a Democratic activist who wants Christie prosecuted over the George Washington Bridge scandal.