Giuliani has emerged as a controversial, but central, figure in recent months after he found himself caught up in the months-long impeachment fight and Trump's efforts to have Ukraine help investigate Democrats.

Trump asked Ukrainian President Volodymyr Zelensky if he would work with Giuliani and help "look into" former Vice President Joe Biden and his son Hunter Biden , according to a partial transcript released by the White House.

The Democratic senators also included multiple reports referencing Giuliani's contacts with DOJ officials as part of an appendix to their letter to Horowitz.

DOJ

"These reports suggest that Mr. Giuliani has used his relationship with the President, including his representation of the President as a private citizen, to gain improper access to attorneys and investigators in the agency, particularly political appointees who serve at the President’s pleasure," they wrote."Various federal laws and regulations, as well aspolicies and procedures, are in place to prevent improper influence and actual or apparent conflicts of interest," they added.