Mayor de Blasio’s communications director is leaving to run his federal political action committee, fueling new speculation that the mayor intends to follow through on his improbable quest for the White House.

Mike Casca took an unpaid leave on Monday to begin working for de Blasio’s political operation, Fairness PAC, making him the first full-time City Hall staffer to move to the fundraising committee.

Meanwhile, de Blasio’s long-serving spokesman — Eric Phillips, who was reportedly cool to Hizzoner’s White House dreams — left for the private sector, taking a gig as a crisis communications expert at public relations powerhouse Edelman.

Casca will be replaced by longtime de Blasio aide Wiley Norvell, who’ll earn $180,000.

Phillips will be replaced by Freddi Goldstein, who served as the spokeswoman for First Deputy Mayor Dean Fuleihan.

Phillips served three years battling for de Blasio, who has famously contentious relationship with the City Hall press corps.

“What a humbling experience,” Phillips tweeted, announcing the news.

Casca — a veteran of Sen. Bernie Sanders’ 2016 campaign — said he will be serving as full-time spokesman for the PAC, which has been paying for de Blasio’s visits to key early primary states like Iowa, New Hampshire and, most recently, Nevada.

He otherwise declined to comment.

De Blasio’s national political forays in the face of horrendous polling numbers, with 76 percent of New York City voters in a recent Quinnipiac University poll urging him not to run in 2020.

His signature $582 million NYC Ferry program has come under intense scrutiny after Comptroller Scott Stringer blocked its attempt to spend $84.5 million to buy on ferries already contracted to the city.

The comptroller’s office also issued subpoenas for City Hall’s $173 million deal to buy 17 buildings from notorious slumlord brothers Stuart and Jay Podolsky for affordable housing.

One City Hall source said the mayor is running to get the national exposure, figuring he’s got nothing to lose.

“He wants to do this because he wants one opportunity on the stage at a debate,” said the source.

“He’s convinced his voice has a chance to break through the noise on this stage. The whole point is to get on stage one time. What’s the downside of that? He’s not passing up that opportunity.”