TRENTON -- Gov. Chris Christie coached Donald Trump prior to the final GOP presidential debate and is becoming a key conduit to the candidate for policy experts, donors and potential backers who now believe he will be the Republican nominee, NJ Advance Media has learned.

Christie, who was initially criticized and ridiculed for endorsing the GOP front-runner after pulling the plug on his own White House bid, has become far more than simply a high-profile presence on Trump's campaign trail.

A member of Christie's inner circle confirmed the governor took time from his 30th wedding anniversary vacation in Florida to help Trump with "debate prep" at the real estate mogul's Mar-A-Lago resort in Palm Beach on March 9, a day ahead of the last Republican debate in Miami.

Christie was invited to help ready Trump after the previous GOP debate in Detroit was widely mocked when Trump and U.S. Sen. Marco Rubio exchanged thinly veiled references to the size of their genitalia.

"It was fairly informal -- Trump doesn't do a 'mock' debate," said the individual with knowledge of the exchange, who is not authorized to talk publicly and requested anonymity.

The next Republican debate was a much tamer affair, and Trump faced far less criticism following it.

Christie has fended off questions about whether he had visited the ultra-exclusive Mar-A-Lago as a guest of Trump during the governor's 30th anniversary vacation in Florida two weeks ago.

At a March 3 Statehouse press conference, Christie told the New Jersey press corps that when he last saw Trump, he told the businessman: "You won't see me for a while, because next week is my anniversary."

But on March 8, Trump asked whether Christie was in the room during a televised press conference at Mar-A-Lago to talk about that day's primaries. The governor did not appear.

When Christie was asked last Friday, he balked at the question.

A spokesman for the governor, Kevin Roberts, declined to address Christie's part in preparing Trump for the GOP debate during his Florida visit or his larger role in the Trump campaign. In an email to NJ Advance Media on Wednesday afternoon, Roberts wrote: "The governor was on vacation with his family."

A spokeswoman for Trump's campaign, Hope Hicks, did not respond to emails and calls seeking comment.

Experts say the disclosure about his role in preparing Trump for the debate suggests an expanding role for Christie in Trump's presidential bid.

"Christie is clearly making the transition from endorser to enabler and positioning himself to be a major player in the Trump camp." David M. Kennedy, a presidential historian.

Edward 'Ted' Newton, who led the research effort for Mitt Romney's vice-presidential vetting process on Christie four years ago, said helping Trump with debate prep illustrates Christie's standing.

"Leading the debate prep, as Christie has, or the VP candidate search, as Dick Cheney did, fosters a strong relationship and a great level of trust," Newton said. "It's natural for that person to see themselves becoming a potential running mate."

Christie took a big risk in endorsing Trump last month. The governor's closest advisers warned him that there could be blow-back, and there was.

Two days after the endorsement, Meg Whitman, the Christie campaign's national finance co-chair, derided it is as "an astonishing display of political opportunism."

When the governor appeared with Trump at a March 1 Mar-A-Lago press conference to discuss his Super Tuesday wins, Christie's awkwardly pained expression became both an internet meme and fodder for "Saturday Night Live."

But now that Trump is rapidly tightening his grasp on the Republican nomination, sources in the governor's camp say Christie is becoming "the conduit back for people who are now trying to help him."

"People are asking, 'Can you help me get involved?' on both the policy front and as endorsers and donors," one said. "They're trying to get there through him, and in that sense, he's become very impactful."

Harvard University professor Joseph S. Nye, Jr., North American chairman of the Trilateral Commission and a foreign policy adviser to Hillary Clinton's presidential campaign, thinks the idea of Christie becoming a portal for Trump's campaign is "certainly plausible," particularly among policy experts.

"There are so few avenues to Trump," said Nye, noting that earlier this month, 100 leading Republican foreign policy and national defense experts signed an open letter calling Trump "utterly unfitted" to be commander-in-chief.

Trump's relative isolation from foreign policy wonks means that Christie serves as a legitimate point of contact, "because he was the first of the (GOP field) to endorse him," Nye said.

Claude Brodesser-Akner may be reached at cbrodesser@njadvancemedia.com. Follow him on Twitter @ClaudeBrodesser.

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