Attorneys for former national security adviser John Bolton John BoltonJudge appears skeptical of Bolton's defense of publishing book without White House approval Maximum pressure is keeping US troops in Iraq and Syria Woodward book trails Bolton, Mary Trump in first-week sales MORE are in touch with House committee staffers about the possibility of his testifying in Democrats' impeachment inquiry into 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, NBC News and CNN reported Friday.

Bolton, whom Trump fired last month, has broken with the president on multiple foreign policy issues, and previous House witnesses have described him as sharply critical of Trump's dealings with Ukraine, which are at the center of the inquiry.

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Former Trump aide Fiona Hill reportedly testified before the House panels last week that Bolton described Trump 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 as a "hand grenade who's going to blow everybody up."

She also reportedly said Bolton told her to tell White House lawyers "I am not part of whatever drug deal Rudy and [chief of staff Mick] Mulvaney are cooking up," referring to an alleged back channel diplomatic effort with Kiev.

Democrats expressed a strong desire to speak with Bolton following Hill's testimony.

“He’s as big a hawk as you’re going to find,” House Intelligence Committee member Rep. Peter Welch Peter Francis WelchShakespeare Theatre Company goes virtual for 'Will on the Hill...or Won't They?' Vermont Rep. Peter Welch easily wins primary Vermont has a chance to show how bipartisanship can tackle systemic racism MORE (D-Vt.) said last week. “And according to the news report, he was shocked and appalled at the run-around of the official channels for a private foreign policy run by Giuliani. So that makes what he has to say of interest to me.”

Spokespeople for the House Foreign Affairs and Intelligence committees declined to comment on whether they were in touch with Bolton's lawyers. The Hill has also reached out to the Oversight and Reform Committee for comment.

The impeachment inquiry was spurred by a whistleblower's complaint that says Trump sought to pressure Ukraine into investigating 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, a leading 2020 contender, and his son, Hunter Biden, in order to gain an edge in next year's election.

Trump has denied any wrongdoing, but a recreated transcript the White House released of a July 25 phone call between him and the Ukrainian president included Trump asking for the Biden probe as a favor, naming Giuliani and Attorney General William Barr Bill BarrFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Why a backdoor to encrypted data is detrimental to cybersecurity and data integrity FBI official who worked with Mueller raised doubts about Russia investigation MORE as administration officials who could assist on the matter. The call came days after Trump delayed the release of hundreds of millions of dollars in military aid to Ukraine.