President Trump Donald John TrumpBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Pelosi: Trump Supreme Court pick 'threatens' Affordable Care Act MORE's personal attorney Rudy Giuliani Rudy GiulianiThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting CIA found Putin 'probably directing' campaign against Biden: report Democrats fear Russia interference could spoil bid to retake Senate MORE told the president that his trip to Ukraine produced "more than you can imagine," a source told The Wall Street Journal.

The former mayor of New York returned to the U.S. Saturday after visiting Kyiv for the first time in two years to interview Ukrainian officials and gather information.

Giuliani is attempting to make a documentary TV series that shows justification for Ukraine to investigate former Vice President Joe Biden Joe BidenBiden says voters should choose who nominates Supreme Court justice Trump, Biden will not shake hands at first debate due to COVID-19 Joe Biden should enact critical government reforms if he wins MORE and his son Hunter Biden as well as Kyiv's role and potential interference in the 2016 general election.

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Hunter Biden was on the board of Ukrainian energy company Burisma Holdings while his father served as vice president.

Both Bidens have repeatedly denied allegations of corruption, and all reports from the U.S. intelligence community have debunked Giuliani's claims that Joe Biden acted in the interest of his son while in office. The theory that Ukraine interfered in the 2016 election has also been debunked.

Giuliani's trip comes as he finds himself in the middle of Congress's ongoing impeachment proceedings.

During the public hearings, multiple witnesses described Giuliani as running a kind of "shadow diplomacy" in Ukraine that diverged from the official goal of the United States' actual diplomats. Giuliani is not and has never been an official employee of the State Department.

The president's lawyer has said that his efforts in Ukraine are justified because he was trying to defend Trump, his client. His dealings in Ukraine have also triggered an investigation by New York federal prosecutors who are reviewing whether or not Giuliani should've registered as a foreign agent, the Journal reports.

Two of Giuliani's associates — Lev Parnas and Igor Furman — have been arrested and charged with campaign finance crimes. The duo has pleaded "not guilty," and Giuliani himself has denied any wrongdoing.

The Hill has reached out to the White House for comment.