A former Justice Department colleague of 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's personal lawyer 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 has said the Giuliani he worked with "would prosecute the Giuliani of today."

"This is certainly not the Giuliani that I know," Giuliani's former top assistant in the Reagan administration, Jeffrey Harris, told NBC News. "I think the Giuliani that I know would prosecute the Giuliani of today."

"There’s a whole apparatus of the United States government that’s set up to deal with foreign officials and Rudy Giuliani’s not one of them," added Harris, who is now a private practice attorney. "To the extent that you could look at this as using government resources for your benefit, there are a number of crimes that this conduct would answer to."

Giuliani served in the Justice Department as the U.S. attorney for the Southern District of New York in the 1980s before becoming New York City's mayor.

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NBC spoke with six of Giuliani's former colleagues, including Harris. None of them came to the Trump lawyer's defense amid recent scrutiny of his interactions with Ukraine and efforts to get the country to launch a probe into former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE.

Bruce Fein, who worked at the Justice Department in the 1980s under former President Reagan, said he believed Giuliani was open to prosecution under federal election laws.

"He was soliciting a foreign government to help Trump’s 2020 campaign. That’s a problem," said Fein, who served as associate deputy attorney general. "Federal election laws make it illegal to solicit anything of value from a foreign government or persons to influence the outcome of an election."

Trump was accused in a recently released whistleblower complaint of using a July call with Ukrainian President Volodymyr Zelensky to try to pressure the foreign leader to investigate Biden and his son for personal gain.

Several details from the whistleblower complaint aligned with a reconstituted readout of the July 25 call released by the White House this week, though Trump has denied wrongdoing, calling the conversation "perfect."

The complaint also alleged that two State Department officials spoke to Giuliani "in an attempt to 'contain the damage' to U.S. national security" over his communication with Ukraine. Giuliani has also denied this.

Reached by NBC for comment on his former colleagues' remarks, Giuliani reportedly texted, "Bullshit."

"They don’t know what they are talking about. What crimes," he added.

In a follow-up phone call, he told the news network that he didn't commit any alleged bribery because he didn't offer the Ukrainians anything valuable.

"Are these guys lawyers or are they morons?" Giuliani said.

He also said he didn't "threaten" Ukraine or "tell them what do do."

"I recommended that it would be a good thing to complete the investigations," he said. "I wasn’t going there to affect the 2020 elections. I was going there to clear my client. It’s totally absurd."