New Jersey Gov. Chris Christie calls on an audience member to ask a question during a town hall meeting at the Hanover Township Community Center in Whippany, N.J. on March 24, 2015.  (AP Photo/Julio Cortez, File)

As New Jersey Gov. Chris Christie tries for a political revival with New Hampshire town halls and Iowa diner stops, he won’t have one of his longtime friends and political advisers at his side.

New Jersey state Sen. Joseph M. Kyrillos, who chaired Christie’s 2009 gubernatorial campaign and ushered his agenda through a Democratic-controlled legislature, is backing former Florida governor Jeb Bush’s all-but-certain presidential bid.

Tim Miller, a Bush spokesman, confirmed Kyrillos’s support Monday as well as a $10,000 donation Kyrillos made in March to Bush’s political-action committee.

The defection of Kyrillos to Bush’s camp is a blow to Christie, who places a premium on loyalty and had hoped to keep his network of allies in New Jersey with him, should he decide to seek the Republican nomination.

Not only is Christie losing a confidant, but a plugged-in operative and former state party chairman who is close with New Jersey’s biggest donors. In 2008, Kyrillos chaired Mitt Romney’s presidential campaign in the state.

Kyrillos is one of several influential Christie associates whose ties to the governor have frayed in recent months. Many power brokers who once cheered his rise are now either hesitant to back Christie as he eyes a campaign for the White House, or shifting allegiances.

Bush has been aggressive in reaching out to New Jersey Republicans whose relationships with Christie have cooled as the governor has clashed with GOP state lawmakers and watched his poll numbers drop.

Bush has stopped short of directly confronting Christie by holding a fundraiser on his home turf. But behind the scenes, he has been wooing, via e-mail, a cadre of New Jersey Republicans, including a group that attended a dinner with Bush at New York’s Union League Club in January.

In February, Kyrillos said in an interview that he was “obviously intrigued” by Bush, and that “time will tell how things evolve.”

Bush political intimates said Monday that he has wooed Kyrillos particularly hard, knowing that the state senator’s break would rattle Christie, who is one of Bush’s rivals for dollars and momentum within the Republican establishment.

Bush’s circle believes Kyrillos’s move could be the start of a wave of other Christie donors and backers formally signing on with Bush, especially as a federal investigation into a bridge-closing scandal that has engulfed Christie’s administration continues and possibly leads to indictments.

Nicholas F. Brady, a former senator from New Jersey and secretary of the treasury under presidents Reagan and George H.W. Bush, has thrown his support to Bush. Former New Jersey governor Thomas H. Kean Sr., Christie’s mentor for years, has been reluctant to rally behind Christie’s likely presidential campaign.

“George H.W. Bush was the last Republican to win here in a general election. He made New Jersey a swing state, and some Republicans think Jeb could do the same,” Kean said an in interview earlier this year.

Meanwhile, Christie’s troubles at home are mounting. A Quinnipiac University poll out Monday shows 56 percent of New Jersey voters disapproving of Christie’s performance as governor, with 38 percent approving — Christie’s lowest marks ever in that poll.

Still, Christie is far from ready to leave the 2016 conversation. Last week, he held multiple events in New Hampshire, which holds the first-in-nation primary, and drew large and enthusiastic crowds to town-hall meetings. On the policy front, he has shifted right, proposing a series of changes to Medicare and Social Security that have won praise from tea party activists -- a bloc long skeptical of him.

Speaking with NBC News on the trip, Christie, with typical bravado, shrugged off Bush’s ascent. “It seems to me like that train has slowed down pretty significantly,” he said.

“Poll numbers go up and they go down based upon your performance, and I am far, far, from finished with my career,” he added.