(CNN) House Democrats are pushing forward on their investigations into President Donald Trump's finances — an area they feel special counsel Robert Mueller's investigation did not fully probe — adding additional senior-level investigative staffers and preparing to go to court to enforce their subpoenas.

The House Intelligence Committee has hired Patrick Fallon, a 25-year FBI veteran who was chief of the FBI's financial crimes section, according to three sources familiar with the matter, adding to their arsenal of staffers with experience prosecuting financial crimes and cases against Russian organized crime. Fallon started this week, according to a committee source.

The House Intelligence and Financial Services Committees are zeroing in on Deutsche Bank as a key part of their investigations into Trump's finances. Trump, his children and his business on Monday sued both Deutsche Bank and Capital One to block subpoenas that the committees have issued, but House Democrats are likely to fight those in court.

"Deutsche Bank is willing to cooperate, but apparently Mr. Trump and others around him are concerned about what those bank records would show," House Intelligence Committee Chairman Adam Schiff told CNN Tuesday. "We're going to have to fight this as vigorously as necessary to make sure that we validate our ability to oversee the administration."

The subpoenas for Deutsche Bank and Capital One are just one element of a broad House Democratic effort to probe Trump's finances — and one that the Trump administration is fighting at every step. The Trump Organization has also sued the House Oversight Committee and his own accounting firm, Mazars USA, after the House Oversight Committee issued a subpoena for years' worth of Trump's financial records from the accounting firm.

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