Trump's lawyer Rudy Giuliani wants Ukraine to investigate Joe Biden's son

Donald Trump's personal lawyer says he is urging Ukraine to open investigations that could benefit the president politically in the United States.

Rudy Giuliani used Twitter on Friday to explain his rationale for travelling to Kyiv to push for two investigations.

One is the origin of special counsel Robert Mueller's investigation into Russian interference in the 2016 U.S. election.

The other is the involvement of Democratic candidate Joe Biden's son, Hunter, on the board of a gas company owned by a Ukrainian oligarch. Giuliani alleges Hunter Biden improperly benefited financially while his father was vice-president and involved in formulating the Barack Obama administration's Ukraine policy.

Giuliani wrote to Democratic Sen. Chris Murphy to "explain to me why Biden shouldn't be investigated," and accused the Democrats of "interfering."

He said on Twitter if the situation "involved [Donald Trump] or his son, it would have been front-page news for weeks."

Giuliani's trip was first reported by the New York Times.

Several Democrats took to social media to say they were appalled Giuliani was openly cultivating a relationship with foreign entities to try to discredit a potential 2020 presidential rival, on the heels of investigations by Mueller and Congress into contacts between Russia and the Trump campaign during the 2016 election against Hillary Clinton.

California Congressman Adam Schiff called Giuliani's trip "immoral, unethical, unpatriotic and, now, standard procedure."

Congress member Jackie Speier, also of California, questioned how the trip was being paid for and said Giuliani's actions could violate the Logan Act, the little-enforced law that bars private citizens from negotiating with foreign governments about disputes or controversies with the United States.

In the Times article, Giuliani argued he's not acting illegally, though he admitted, "somebody could say it's improper."