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 lit into Democrats on Monday following the announcement that three House committees are launching a broad investigation into whether President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE, Giuliani and others sought to exert pressure on the Ukrainian government to target former Vice President Joe Biden.

Giuliani, the president's personal lawyer, questioned the legitimacy of their probe while accusing Democrats of waging a politically motivated inquiry that he equated to harassment.

"This is not legitimate. It is harassment — a political operation by the Democratic National Committee, not by Congress," Giuliani said during a Thursday phone interview with The Hill. "They need three committees to do this, and there is only one of me."

Intelligence Committee Chairman Adam Schiff (D-Calif.), Oversight and Reform Committee Chairman Elijah Cummings (D-Md.) and Foreign Affairs Committee Chairman Eliot Engel (D-N.Y.) in joint letters demanded documents from the White House and State Department earlier Monday related to whether Trump and Giuliani sought to pressure Ukraine to target Biden, a front-runner for the 2020 Democratic presidential nomination.

They set Sept. 16 as the deadline for documents to be turned over.

ADVERTISEMENT

Giuliani, who gained a reputation as a mob-buster during his time as a U.S. attorney in New York, spouted off a series of allegations that Biden used his diplomatic might to interfere in a Ukrainian investigation, during which his son was under scrutiny.

Biden has insisted there was no wrongdoing.

Giuliani vowed to take Democrats to court and use this opportunity to expose Biden and the "corrupt Washington press" corps, which he claimed had been shielding Biden.

"I'm going to use this as an opportunity to highlight what phonies they are, trying to intimidate and harass me," he said while describing the Democratic probe as a "little pimple" compared to the "major massive scandal" involving Biden and Ukraine.

"I just stumbled on this. Joe got himself in trouble," he continued. "He's so stupid. I didn't know his family was cashing in as much as he did."

When Giuliani was asked to respond to criticism that he is improperly using his position as Trump's personal lawyer to interfere in foreign matters in an attempt to help his boss out politically, he replied, "So what?"

"I'm doing that, and Biden takes millions out of China?" he asked, pointing to another controversy that Biden's critics have used to claim his family has profited off his diplomatic work.

Giuliani also defended his involvement, stating that he is helping his client "legally" by trying to encourage the new Ukrainian president, Volodymyr Zelensky, to investigate whether the Ukrainian government sought to hurt Trump's campaign during the 2016 election, before he took office.

Democrats' announcement of the probe comes after The Washington Post’s editorial board reported late last week that Trump is using $250 million in U.S. military aid as leverage to pressure Zelensky's administration into opening a corruption probe into Biden.

Giuliani told The New York Times in August that he was acting as a private citizen when he held phone calls and had an in-person meeting with Andriy Yermak, a top Zelensky representative. He has claimed that he was taking up the matter to help the country fight against corruption, but doing so highlights how Giuliani has inserted himself into international affairs and used his status as the president’s personal lawyer to help his boss politically.

“I can’t really evaluate that — whether my involvement in it makes it worse or better,” Giuliani told the Times in an interview last month, acknowledging that he “strongly urged” Yermak to “just investigate the darn things.”

“I can’t see how advocating for an investigation of two alleged crimes puts too much pressure on them, other than to do the right thing,” he added.

Yermak, Democrats noted in their letter, has publicly stated that he was not sure "whether Mr. Giuliani was representing Mr. Trump in their talks."

Giuliani, who said the State Department was aware of his meetings with the Ukrainian representative, would not tell the Times whether the president signed off or knew about this latest effort.

Still, news of the probe appeared to further embolden Giuliani, who attacked the three Democratic chairmen personally in addition to Biden and his son.

"They are amateurs at what I'm a professional at: investigating crimes," Giuliani told The Hill.

"This is even dumber than calling in Mueller," Giuliani added, referring to the lackluster testimony Democrats received from former special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE earlier this year, in which no new information was revealed.

News of the probe comes as Democrats in the House are broadening their investigations into the Trump administration and considering whether to introduce articles of impeachment.

Giuliani and the White House have shown a fiery fervor in fighting back, whether it is challenging Democrats to investigate them or stonewalling their investigative requests under claims of executive privilege.