Former White House 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 opposed the phone call between 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 and Ukrainian President Volodymyr Zelensky at the center of an impeachment inquiry launched by House Democrats, NBC News reported Monday.

Three current and former administration officials told the network that Bolton was opposed to the call because he was concerned Trump wasn’t coordinating with advisers on what to say and might air personal grievances.

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Officials reportedly noted that Bolton did not listen in on the call.

The Hill has reached out to the White House for comment.

In the conversation on July 25, Trump pressed Zelensky to investigate 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 and his son Hunter Biden.

A partial transcript of the call released by the White House last week confirmed the request from Trump.

The call gained attention following reports of a whistleblower complaint from within the intelligence community that focused on it.

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.) formally launched an impeachment inquiry last Tuesday and committee chairs have already begun requesting related documents.

Bolton was ousted as national security adviser last month amid policy disagreement with Trump.

In his first public speech since leaving the administration, he said on Monday that he does not believe North Korean leader Kim Jong Un Kim Jong UnNorth Korean leader Kim apologizes over killing of South Korean official Pelosi knocks Trump over refusal to commit to peaceful transfer of power Satellite images indicate North Korea preparing for massive military parade MORE will give up his nuclear weapons in a deal with the United States, contradicting Trump's position on the issue.