US President Donald Trump ordered the firing of special counsel Robert Mueller last June, only to back down when his own White House lawyer threatened to resign, US media claim.
White House counsel Donald McGahn said the sacking would have a "catastrophic effect" on the presidency, the New York Times reports.
Mr Mueller is leading an inquiry into whether the Trump campaign colluded with Russia to influence the election.
Both Moscow and Mr Trump deny this.
The deputy attorney general appointed Mr Mueller, a former FBI director, as special counsel last May. His inquiry is also looking at whether the president and his inner circle tried to obstruct justice after the firing of FBI director James Comey.
The special counsel learned of his near-dismissal in recent months, while his team interviewed past and present White House officials, the New York Times reports.
As speculation mounted that Mr Mueller could be building an obstruction case against the president, Mr Trump allegedly argued that he had three conflicts of interest that should stop him heading the inquiry.
These were said to be:
- That Mr Mueller abandoned his membership of the Trump National Golf Club in Sterling, Virginia in 2011, over a fee dispute.
- That Mr Mueller could not be impartial as he had worked for a law firm that previously acted for Jared Kushner, the president's son-in-law.
- That the investigator had been interviewed to return to his former job as FBI director the day before he was appointed special counsel in May 2017.
The White House did not immediately comment on the New York Times report, which cited four unnamed sources. A later story in the Washington Post cited two people familiar with the episode.
US news outlets had hinted in December that the president might fire the special counsel. His opponents in the Democratic party would see any such move as a bid to stifle justice, and it could trigger an effort to impeach Mr Trump.
In response to the latest reports, Senator Mark Warner, the Democratic vice-chairman of the Senate intelligence committee, warned that "firing the special counsel is a red line that the president cannot cross".
"Any attempt to remove the Special Counsel, pardon key witnesses, or otherwise interfere in the investigation, would be a gross abuse of power," he said.
Mr Trump said on Wednesday that he was willing to be questioned under oath by the Mueller inquiry.
He told reporters he was "looking forward" to it, subject to the advice of his lawyers, and that an interview could happen within two to three weeks.