Robert Mueller calls Trump's bluff, zeroes in on financial records

But that is not the only major line of investigation Mueller is pursuing.

According to a report by Bloomberg News on Tuesday, Mueller has issued a subpoena to Deutsch Bank for the financial records not only of Trump but of his family as well.

Deutsche Bank, headquartered in Germany, has long been rumored to be the conduit Russia used to make any financial arrangements with Trump. The bank has paid over $600 million in fines to U.S. and British regulators for facilitating Russian money laundering. Not much is known about Trump’s dealings with Deutsche Bank, except that he owed it $300 million for real estate dealings prior to taking office.

The bank had previously rebuffed requests from Democrats in Congress to open its books, but is now cooperating with Mueller’s subpoena.

This development is significant because in July, Trump told New York Times reporters he believed any attempt by Mueller to probe his finances was a “red line” and would be a “breach” of what the Office of Special Counsel has been tasked to do.

SCHMIDT: Last thing, if Mueller was looking at your finances and your family finances, unrelated to Russia — is that a red line?

HABERMAN: Would that be a breach of what his actual charge is?

TRUMP: I would say yeah. I would say yes.https://t.co/uT2RxuLu2B https://t.co/sTJlvyWYKP

— Greg Sargent (@ThePlumLineGS) December 5, 2017

Legal experts say that Trump is wrong. But regardless, Mueller is calling that bluff — and it remains to be seen whether Trump will make good on his threats against Mueller, the way he did against Comey.

Republican leaders in Congress have repeatedly stated there is no need for legislation to protect Mueller from termination. That assurance is about to be tested.