It’s a “devastating turning point” and possibly the “beginning of the end” of Gov. Andrew Cuomo’s 30-plus-year political career.

That’s the profound impact of US Attorney Preet Bharara’s corruption probe of Cuomo’s longtime friend and top aide Joe Percoco — who was tighter with the governor than even members of his own family, top state Democrats told The Post.

“Joe was even closer to Cuomo than [girlfriend] Sandra Lee, closer than his sisters and even his brother Chris. Joe was always there with him, for God’s sake,’’ said a prominent Democrat who has known Cuomo for years.

In a move widely seen as a pre-emptive effort to put his own “spin’’ on the federal probe, Cuomo announced late Friday that an investigation was being launched into “undisclosed conflicts of interest by some individuals which may have deceived state employees’’ involved in economic development programs.

The announcement, which came as Bharara’s probe of Percoco became public, stunned many close to Cuomo because it appeared that the governor was, as a Cuomo administration source put it, “just throwing Joe under the bus, which seemed incredible to everyone and suggested how serious all of this is.’’

Administration insiders quickly began asking if Percoco — whose career and relationship with the governor goes back to the days of Gov. Mario Cuomo — could have, as investigators suspect, illegally pocketed some $150,000 from contractors without Cuomo knowing about it.

“Do you think Joe would have done something like this without checking with Andrew and letting him know what was happening?’’ asked a longtime Cuomo associate.

“I find that impossible to believe,’’ the source continued.

Influential Democrats predicted Cuomo’s hopes of being the keynote speaker at this summer’s Democratic convention, already a long shot, will be dashed by Bharara’s probe.

They said Cuomo’s barely disguised hope to someday run for president would likely be ruined if Bharara brings criminal charges against Percoco.

And Cuomo’s plans to run for re-election in 2018 would be seriously affected — possibly prompting another Democrat, like Attorney General Eric Schneiderman, to launch a primary challenge.

Another huge question hovering over the governor is whether Percoco, privy for years to the intimate workings of the Cuomo administration, might have information that would be of interest to Bharara — which he might be willing to trade for leniency.

“This is a devastating turning point for Andrew that could be the beginning of the end’’ of his career, said a Democrat who once counted himself among Cuomo’s strongest supporters.

Albany insiders predict that state Board of Elections Chief Enforcement Officer Risa Sugarman’s days are numbered if Manhattan DA Cyrus Vance Jr. doesn’t agree with her recently leaked finding that Mayor Bill de Blasio and several political aides broke the law by raising large sums of campaign cash for state Senate candidates.

“This charge against the mayor is so serious, a felony, and the leaking of what was supposed to be a confidential memo so outrageous, that if Vance concludes that no crime was committed, then Risa will have to go,’’ said a senior state Democrat who, like Sugarman, has close ties to Cuomo.

Of course, if Vance concludes a crime was committed and seeks an indictment against de Blasio, Sugarman could go down as the state bureaucrat who brought down a mayor.