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 on Monday said that he can’t say for certain that Trump didn’t threaten Ukraine aid when he spoke to that country's president about an investigation 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's son.

Giuliani, who is acting as the president's personal attorney, during an interview Monday with Fox Business first said reports that Trump threatened to cut aid was “a false story,” but then backtracked when pressed.

“Did the president threaten to cut off aid to the Ukraine?” Fox Business host Maria Bartiromo Maria Sara BartiromoBiden's team says he views election against Trump as 'Park Avenue vs. Scranton' Ex-NFL player running for House as Republican blasts Democrats as 'narcissists and sociopaths' Cruz says he wouldn't accept Supreme Court nomination MORE asked Giuliani during the interview.

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“No, no, that was a false story,” he responded.

“One hundred percent?” the host asked Giuliani.

“Well, I can’t tell you if it’s 100 percent,” Giuliani said.

BARTIROMO: Did the president threaten to cut off aid to Ukraine?

GIULIANI: No, no. That was a false story.

BARTIROMO: 100 percent?

GIULIANI: Well I can't tell you if it's 100% percent. pic.twitter.com/ApBGsK6kZz — Aaron Rupar (@atrupar) September 23, 2019

The Wall Street Journal on Friday reported that Trump repeatedly pressured Ukraine President Volodymyr Zelensky to investigate Biden's son Hunter Biden, who had been doing work in Ukraine.

Biden is running for the Democratic presidential nomination and is seen as the front-runner. Polls have shown him ahead of Trump in head-to-head match-ups. No evidence has emerged of any impropriety on the part of the former vice president, even as Trump has made calls for him to be investigated.

The Journal reported that its source said the issue of U.S. military aid to Ukraine didn't come up in the call, but lawmakers are now focused on whether there was any connection between aid and the pressure on Zelensky.

Trump has acknowledged discussing Biden and the investigation with Zelensky but has repeatedly said he did nothing wrong while dismissing Democratic criticisms.

The allegations over Trump’s call with Ukraine has led to renewed calls for an impeachment inquiry by some House Democrats. Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) warned of a new stage of investigation on the matter but did not use the word impeachment in a letter sent to members on Sunday.

She did say the matter needed to be handled immediately, noting a whistleblower had brought up the matter and the the Justice Department's inspector general had labeled it an urgent matter.

The contents of the whistleblower complaint have not been revealed to Congress, which is another issue that has rankled Democratic lawmakers. Pelosi has joined Democrats in calling for the complaint to be released to Congress.