The world is talking about Donald Trump's relationship with Deutsche Bank. Here's why it's drawing intense scrutiny.

Trump has worked to keep financial documents related to him and his family from being made public. His lawyers tried to block the subpoena sent to Deutsche, but the House of Representatives declined the motion.

Trump has been mostly successful in keeping his more recent tax returns away from the public eye. A New York Times report on leaked tax records from 1985 to 1994 detailed $1.17 billion in reported losses from Trump's businesses. The documents also suggested Trump may have skirted federal income tax requirements for two decades.

The report mirrored a 2016 piece by The Times that showed Trump claimed $916 million losses in his 1995 personal tax filing. The piece was published ahead of a presidential debate, during which Trump said paying no taxes made him "smart."

House Democrats have long coveted Trump's tax returns. As Emily Stewart at Vox recently wrote, "Trump's tax returns have been treated as a Holy Grail that would unlock the secrets of his wealth and, depending on where you fall on the political spectrum, potentially reveal him as a fraud or as having unsavory ties to foreign interests."

But as The Washington Post recently reported, Democrats had become resigned to the idea that they might not get access to the returns before the election.

So in revealing that it possesses some of the tax records Congress is seeking, Deutsche Bank marked a step forward in investigations into Trump's finances, even as the bank did not identify whose records it has.

MSNBC's Lawrence O'Donnell claimed later on Tuesday he heard from a source "close to Deutsche Bank" that Trump's loan documents with Deutsche Bank reveal Russian oligarchs as co-signers. He added the Russian billionaires "are close to Vladimir Putin."

"If true, that would be a significant factor in Vladimir Putin's publicly stated preference for presidential candidate Donald Trump over presidential candidate Hillary Clinton," O'Donnell said.

The host did not claim to be able to corroborate the source's statement, and later walked it back.