The whistleblower complaint that has triggered a tense showdown between the U.S. intelligence community and Congress involves President Trump’s communications with a foreign leader, according to two former U.S. officials familiar with the matter.

President Trump on Thursday ripped reports that he made a promise to a foreign leader so troubling that a whistleblower reported it to the intelligence community’s in-house watchdog — calling them “Fake News” and “Presidential Harassment!”

“Another Fake News story out there – It never ends! Virtually anytime I speak on the phone to a foreign leader, I understand that there may be many people listening from various US agencies, not to mention those from the other country itself. No problem!” Trump wrote in one of a series of three tweets.

House intelligence committee chairman Adam Schiff vowed Thursday he's willing to sue the Trump administration over a dispute about the contents of as-yet unknown complaint to the intelligence community's official watchdog.

Schiff told reporters after a closed-door meeting with the inspector general, Michael Atkinson, that the Justice Department has opined that the material is shielded by privilege and can be withheld from lawmakers.

Not so, Schiff argued, and "if we have to go to court to get this, we will have a good case."