Rudy Giuliani said President Trump would have violated the Constitution if he had not urged Ukrainian President Volodymyr Zelensky to investigate allegations of corruption by former Vice President Joe Biden.

The former New York mayor, who is Trump's personal attorney, appeared on Fox News late Saturday to defend Trump's July 25 call with Zelensky, the subject of an intelligence community whistleblower complaint, and speak out about the Democratic-led House's impeachment inquiry and the abrupt resignation of an American diplomat at the center of the controversy.

"In the case of evidence of serious criminal conduct, they have the obligation to do it. In fact, if the president hadn't done it, he would have violated Article II, Section 3 of the Constitution to take care that the laws are faithfully executed," Giuliani told host Jeanine Pirro, who asked if world leaders have the right to ask each other a favor.

Giuliani, 75, appeared to be referring to the part of Article II, Section 3 that says, "He shall take care that the laws be faithfully executed, and shall commission all the officers of the United States."

At issue is the time Biden boasted in 2018 that, as vice president, he threatened to withhold $1 billion in U.S. loan guarantees if Ukraine did not fire its top prosecutor, Viktor Shokin.

Giuliani has spent months urging Ukraine to investigate possible Ukrainian election interference and whether Biden wanted Shokin fired because Shokin reportedly undertook an anti-corruption investigation into Ukrainian oligarch Mykola Zlochevsky, the owner of Burisma Holdings, which employed Biden’s lobbyist son, Hunter Biden, as a board member.

However, Shokin was widely seen by the United States and Europe — and inside Ukraine — as ineffective, corrupt, and a hindrance to Ukraine’s progress. Ukraine’s Parliament removed Shokin in 2016.

Notes on the Trump-Zelensky call, released last week, show Trump asked for Ukraine's help in investigating a number of matters, including urging Zelensky to look into whether there was any Ukrainian involvement in the 2016 election and suggesting that the Ukrainians investigate allegations of corruption related to the Bidens. He specifically urged Zelensky to speak with Giuliani and Attorney General William Barr about this. The DOJ denies Barr has spoken with anyone in Ukraine. It was reported on Saturday that Barr was "surprised and angry" that Trump lumped him together with Giuliani during the call.

Although Trump and his defenders argue the notes show no evidence of a "quid pro quo" by leveraging millions of dollars in delayed U.S. military aid to Ukraine in order to pressure Zelensky, House Speaker Nancy Pelosi initiated a formal impeachment inquiry last week after the president admitted he did bring up Biden to his Ukrainian counterpart.

Prompted to react to the Democrats' rationale, Giuliani argued there is not sufficient evidence to impeach a president.

"High crimes and misdemeanors. Unless we want to impeach because we don't like the way a guy talks or looks or feels. If you read the Constitutional Convention and the Federalist Papers, there is no doubt there has to be a discernible crime and it has to be an important, serious crime. And there is no crime here. There is nothing wrong here," Giuliani said.

He noted that Zelensky has denied he was pressured in his phone call with Trump.

Giuliani was asked about Kurt Volker, the U.S. envoy to Ukraine, who was named in the whistleblower complaint as communicating with Giuliani about meeting with Ukrainians who abruptly resigned on Friday. Giuliani asserted that the State Department gave him the green light to carry out his mission in Ukraine and that he had been fighting corruption not seeking dirt on the Bidens.

He said Secretary of State Mike Pompeo, who has been subpoenaed by House Democrats, has nothing to worry about and that his staff "did nothing wrong." The former New York City mayor said he assumed Pompeo knew about his communications with Volker and claimed he spoke with the secretary about it afterwards and Pompeo said he had some knowledge of what was going on.

After dismissing the idea that Volker could have been a source for the whistleblower complaint, Giuliani said he was "very sorry" for what happened to Volker, describing him as "very professional, very intelligent, very patriotic." Asked why Volker resigned, Giuliani responded: "I don’t know, maybe they got angry he brought me in.”

Volker is expected to appear in a deposition before three House committees next week.