Giuliani's shadow diplomacy in Ukraine was brought up in a whistleblower complaint filed by a member of the intelligence community in August of this year.
The whistleblower complaint, which alleged the president used his power for political gain, became the impetus for the House of Representatives to launch an impeachment inquiry.
The House impeachment inquiry unearthed Giuliani's apparent role in a dirt-digging mission in Ukraine and his alleged efforts to pressure the Ukrainian government to announce politically-motivated investigations, including into former Vice President Joe Biden, a political rival, and his son Hunter.
Giuliani has denied any wrongdoing.
The House passed two articles of impeachment — one for obstruction of Congress, and the other for abuse of power — earlier in December.