President Trump lashed out at Congress Thursday as it investigated a whistleblower complaint allegedly involving a “promise” Trump made to a foreign leader.

Trump labeled “fake news” and “presidential harassment” a Washington Post story describing the complaint about the alleged “promise,” details of which were not revealed.

The complaint was filed by an intelligence official and is under investigation by the inspector general of the intelligence committee, Michael Atkinson, who testified Thursday behind closed doors before a congressional oversight committee about the handling of the complaint, which had been marked “urgent” and involved “serious misconduct.”

“Virtually anytime I speak on the phone to a foreign leader, I understand that there may be many people listening from various U.S. agencies, not to mention those from the other country itself. No problem!” Trump tweeted in part. “Knowing all of this, is anybody dumb enough to believe that I would say something inappropriate with a foreign leader while on such a potential ‘heavily populated’ call?”

Rep. Mike Quigley, D-Ill., said after the intelligence briefing the complaint actually was based on multiple incidents.

In recent weeks, Trump has had contact with five foreign leaders: Russian President Vladimir Putin, North Korean dictator Kim Jong Un, the prime ministers of Pakistan and the Netherlands and the emir of Qatar. The complaint was filed Aug. 12 but it was unclear whether the it involved any of those five leaders.

Trump has had a rocky relationship with the intelligence community since coming into office. In the early days he indicated he had more faith in Russian denials about meddling in the 2016 presidential election than in U.S. intelligence assessments detailing Russian actions, which the Mueller report outlined in great detail.

House Intelligence Committee Chairman Adam Schiff, D-Calif., announced Wednesday Director of National Intelligence Joseph Maguire would testify publicly about the issue Sept. 26.

Maguire neglected to transmit the complaint to Congress in a timely manner as required by law, allegedly because he believes the details of the complaint are outside his jurisdiction, the Washington Post reported. Maguire consulted the Justice Department. In a letter to Schiff, he said the complaint involved “potentially privileged communications by persons outside the intelligence community,” presumably Trump himself.

In a letter to Schiff earlier this week, DNI general counsel Jason Klitenic said the law did not require that the complaint be turned over to congressional intelligence committees.

Schiff said he's not sure whether the Post report is true but the administration is actively trying to keep information from getting to Congress.