One of the great mysteries of the business world is why Deutsche Bank lent financial pariah Donald Trump $2 billion over two decades, when other firms treated him like an infectious disease capable of wiping out entire populations. Thanks to Democrats’ newly obtained subpoena power, the answer may be revealed through the “extensive internal documents and communications about Mr. Trump” the bank is expected to start handing over to congressional committees next month. In the meantime, however, a report from The New York Times about the president’s relationship with the German lender has shed some light on the matter. For one, Deutsche had a “ravenous appetite for risk,” including the risk of doing business with a guy whose name was synonymous in some quarters with bankruptcy. As a result, reporter David Enrich writes, bank executives were happy not only to ignore repeated, glaring red flags, but to go along with Trump’s cornucopia of financial lies.

Enrich brings the receipts. In 2004, shortly after Trump Hotels & Casino Resorts defaulted on hundreds of millions of bonds, causing steep losses for Deutsche clients, Trump asked the bank’s commercial real-estate group to lend him more than $500 million to build a 92-story skyscraper in Chicago. It did, but not before employees determined, among other things, that Trump was massively inflating his assets.

Mr. Trump told Deutsche Bank his net worth was about $3 billion, but when bank employees reviewed his finances, they concluded he was worth about $788 million, according to documents produced during a lawsuit Mr. Trump brought against the former New York Times journalist Timothy O’Brien. And a senior investment-banking executive said in an interview that he and others cautioned that Mr. Trump should be avoided because he had worked with people in the construction industry connected to organized crime.

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In patented Trump fashion, shortly before the bulk of the loan was due in November 2008, he sued the bank to get out of repaying, demanding $3 billion in damages and arguing that Deutsche had, in part, caused the financial crisis and was therefore to blame for his inability to sell hundreds of condo units. The firm countersued, and investment-banking executives severed ties with the real-estate developer. However, other divisions of the company were more than happy to go back for more.