Today we learn that special counsel Robert S. Mueller III is following President Trump's money.
It said investigators wanted information on certain money and credit transactions, and that key documents had already been handed over.
Deutsche Bank, which has loaned the Trump organization hundreds of millions of dollars for real estate ventures, said it would not comment on any of its clients.
Trump has done billions of dollars' worth of business with Deutsche Bank in the past 20 years; he has previously said that he would consider Mueller looking into his finances beyond any connection to the Russian Federation investigation "a violation".
There was no immediate response to the Deutsche Bank subpoena from Trump's lawyers.
Why is Deutsche Bank so important?
Holding such debt, particularly if some of it was or is coming due, could potentially give Russian banks some leverage over Trump, especially if they are state-owned, said a second US official familiar with Russian intelligence methods. The one exception was Deutsche Bank, to which Trump owed $364 million as of the end of past year.
Trump's relationship with Deutsche Bank stretches back some two decades and the roughly $300 million he owed to the bank represented almost half of his outstanding debt, according to a July 2016 analysis by Bloomberg.More news: Yemen's Ali Abdulla Saleh killed for 'treason' - Houthi rebels
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At this point, we don't know exactly what Mueller is looking for in the Deutsche Bank records. Trump owes the bank about $300m in loans that were extended to him before he became president.
In an interview this past July Trump told The New York Times that Mueller would cross a red line if he examined his or his family's finances. And he also has deep financial entanglements with alleged Russian oligarchs and mobsters. Former Trump campaign chairman Paul Manafort, his deputy Rick Gates and former campaign foreign policy adviser George Papadopoulos have also been charged.
Trump has consistently denied any collusion between his campaign and Russian Federation and has stated that he did not have any business dealings in Russian Federation.
- There's the question of whether obstruction of justice took place, for which evidence is growing by the day.
The Trump International Hotel is shown on August 10, 2017 in Washington.
Interested in Russia Investigation?
In that tweet about Flynn, Trump closes by saying, "There was nothing to hide!"
During his White House campaign, Trump said he would seek to improve ties with Russian President Vladimir Putin, which had been frequently strained during President Barack Obama's administration.