Mayor Rahm Emanuel raised $433,391 over the last three months, thanks to support from investment bankers, law firms that benefit from city business and unions that once spurned him.

With $4 million raised since his 2015 re-election and $1.6 million in the bank, Emanuel has only just begun to flex his notorious fundraising muscle.

But, the quarterly report filed this week shows that a mayor who raised $1.6 million last year has continued his slow, but steady pace of rebuilding his campaign war chest.

The report filed with the Illinois State Board of Elections shows hefty contributions from clout-heavy law firms that have benefited from city business.

They include Winston & Strawn ($20,000); Schiff Hardin ($15,850); and Latham & Watkins ($8,600).

During the 2011 mayoral campaign, John Coli Sr., the now indicted former head of Teamsters Joint Council 25, provided early and pivotal support for Emanuel while most other union leaders either took a pass or endorsed vanquished mayoral challenger Gery Chico.

Labor warmed to the mayor’s 2015 re-election bid and that trend has continued, the records show.

Emanuel reported $112,000 in contributions from organized labor in the last quarter. That includes: $50,000 from the Finishing Trades of Chicago PAC; $25,000 from Unite Here Local 1 PAC and $10,000 from Painters District Council 14.

Venture capital and investment banking continued to provide a deep well of support for Emanuel, who made $18 million in just 2.5 years as an investment banker after leaving the Clinton White House.

Major contributors included: Broadhaven Partners ($30,600); Beacon Capital Partners ($22,400); Bryan and Cristina Cressey ($11,200); CMR Ltd. Partnership ($11,200) and William Brodsky of Cedar Street Asset Management ($4,600).

Other noteworthy contributions came from: Hollywood producer Harvey Weinstein ($5,600); executives of Garrett Brands ($15,000); former Corporation Counsel Stephen Patton and his wife, Linda ($11,200) and Jim Messina, the manager of former President Barack Obama’s 2012 re-election campaign ($5,600).

The mayor’s quarterly list of donors also includes: RLM Management Group ($11,100); Willow Street Maintenance ($11,100); Linked In Executive Reid Hoffman ($5,600) and the Burnham Committee, one of several political funds controlled by Finance Committee Chairman Edward Burke (14th) ($5,600).

Two years ago, Emanuel was forced to spend $24 million to survive Chicago’s first mayoral runoff against County Commissioner Jesus “Chuy” Garcia, a relative political unknown.

Ald. Scott Waguespack (32nd), chairman of the City Council’s Progressive Caucus and one of Emanuel’s most outspoken critics, said the mayor is likely to need $30 million to have any hope of getting re-elected.

“He can get it from Hollywood, where he went last time. He can get it from people outside the city or people who are not vested in the neighborhoods. He’ll be able to scrape that together,” Waguespack said.

“He’s made a lot of decisions that have benefited a lot of his smaller constituency, the benefactors. So, he’ll be able to tap into them pretty much unlimited. But, it’s gonna come from a very narrow band of people.”

But Waguespack argued if a credible challenger emerges, and can raise as much as $10 million, that person could give Emanuel a run for his money.

The bill of particulars against Emanuel is so long, campaign commercials against him almost write themselves, Waguespack said.

“Covering up Laquan McDonald. The taxes without showing where we’re gonna end up with those. The crime issues without an answer. Police reform. People have different opinions on that. But it’s the way he’s gone about it behind closed doors without talking to the people of the city who are most affected,” Waguespack said.

Peter Giangreco, Emanuel’s political consultant, refused to comment — either on the mayor’s fundraising or on Waguespack’s take on Emanuel’s vulnerability.

Ald. Pat O’Connor (40th), the mayor’s City Council floor leader, stressed that Emanuel has not yet decided whether to seek a third term.

But, O’Connor said, “I’m confident that if he determines he’s gonna run, he’ll have the resources to do it.”