Mr. Cohen borrowed from a half-dozen banks and credit unions to buy taxi medallions. Then he used the medallions as collateral to borrow more money to buy more medallions, former colleagues said. He quickly amassed 30 medallions, each then worth about $250,000, but racked up millions in debt.
Together, the two men managed 260 cabs in the late 1990s and early 2000s, some for other owners. Drivers paid them $100 a shift. Millions of dollars in cash flowed in. Mr. Cohen at some point began carrying a licensed pistol in an ankle holster.
In 2007, Mr. Cohen started working for the Trump Organization. While there are varying accounts of how he met his new boss, Mr. Trump said Mr. Cohen appeared on his radar after he began buying up properties in Trump buildings — by then, Mr. Cohen’s office addresses included tony Fifth Avenue locations. For his part, Mr. Cohen has said that the job came after he helped resolve a board dispute at one of the Trump buildings where his family owned several units.
Mr. Cohen became a roving fixer for Mr. Trump. In his first year on the job, he and Ivanka Trump kicked the tires on a potential golf course development project in Fresno, Calif. A year later, he was named chief operating officer of Affliction Entertainment, a mixed martial arts venture that Mr. Trump had started. Mr. Cohen traveled to the former Soviet bloc on Mr. Trump’s behalf, visiting Georgia in 2010. He even scouted out Iowa for Mr. Trump ahead of the 2012 presidential campaign and set up a website called ShouldTrumpRun.org.
During Mr. Trump’s 2016 campaign, Mr. Cohen pursued plans for a Trump Tower in Moscow with Felix Sater, a Russian immigrant and friend of Mr. Cohen, who had worked on other real estate development deals with Mr. Trump and had explored possible ventures in Russia. Mr. Trump and Mr. Cohen worked with Mr. Sater even after his role in a stock manipulation scheme involving Mafia figures and Russian criminals was revealed. (Mr. Sater pleaded guilty and became an informant for the F.B.I. and intelligence agencies.)
While juggling his Trump duties, Mr. Cohen turned over management of his cabs to Mr. Garber in 2006 and received as much as $1 million per year, legal records show. After a falling-out with Mr. Garber, Mr. Cohen became partners with Evgeny Freidman, known as Gene, an immigrant from St. Petersburg, Russia, who had assembled a large taxi fleet.
Both of Mr. Cohen’s taxi partners had a history of legal run-ins. Each has been made to pay more than $1 million for overcharging their drivers, according to the New York State attorney general. Former business partners also accused each of them of forging signatures, stiffing lawyers and dodging debt collection efforts.
The Chicago authorities found that Mr. Garber and his taxi businesses used 180 unauthorized cars as taxis in that city; he agreed to pay a fine of nearly $1 million.
In 2016, a federal judge found that Mr. Freidman had transferred more than $60 million into offshore trusts to avoid paying debts. Last April, New York City regulators barred him from continuing to manage medallions. He currently is awaiting trial in Albany on charges he failed to pay $5 million in taxes.
Despite the prohibition issued by city regulators, Mr. Freidman is still managing Mr. Cohen’s medallions, both men have said.
“Cohen associated himself with the most reckless and greedy players in the industry,” said Bhairavi Desai, the executive director of the Taxi Workers Alliance, a group that represents cabdrivers. “They have simultaneously worked to inflate the value of their medallions and rip off their drivers.”
Patrick J. Egan, a lawyer for Mr. Freidman, said his client denies all the allegations against him. Mr. Freidman, he said, has been the victim of “fabricated claims” by former colleagues and politically motivated prosecutors.
Mr. Garber did not respond to requests for comment.
From 2009 to 2014, Mr. Cohen — by then a trusted member of the Trump Organization — plowed $5.7 million into 22 Chicago taxi medallions, records show.
The investments were ill timed. The ascent of ride-hailing services like Uber and Lyft decimated the value of medallions. Since 2014, Mr. Cohen’s companies have been falling behind on taxes. Over all, his taxi businesses in New York and Chicago owe more than $375,000 for a variety of tax, insurance and inspection problems, according to records. Fourteen of his 54 cabs were suspended.
But even as the industry has buckled, Mr. Cohen has continued to use his medallions as collateral to borrow money. In December 2014, with his medallions worth $35 million, he took out loans totaling at least $20 million from Sterling National Bank and Melrose Credit Union, according to a banker who reviewed the transactions. (Documents related to both lenders were among the materials sought by federal prosecutors in their search warrants.)
In 2016, Mr. Cohen went so far as to dabble in financial engineering. He spoke to investors about pooling distressed loans that financed taxi medallion purchases, repackaging them and selling them to investors, according to a person with direct knowledge of the discussions. He also explored buying up such loans at a bargain price in anticipation that their value would recover, the person said. The outcome of those discussions was not clear.
The financial maneuvering has continued even after the federal search warrants were executed. On April 24, Mr. Cohen refinanced all 16 of his taxi company medallion loans. The transactions, with Sterling National Bank, appeared to extend the due dates on the loans by four years, according to public filings on the refinanced loans. And they added a new, unusual source of collateral: If Mr. Cohen were to default, Sterling would have the right to any money that Mr. Freidman owes Mr. Cohen.
Many of Mr. Freidman’s taxi companies have declared bankruptcy. Asked about the loans, Mr. Freidman’s lawyer said his client had “no assets” that could be used as collateral.