Donald Trump has a long history of bizarre interactions with foreign leaders. For the last two and half years, he’s regularly trashed allies of the United States, berating everyone from Australia to Canada to Germany to France, pulling out of trade deals, calling them deadbeats, and, recently, canceling a visit to Denmark because he was told he couldn’t buy Greenland. On the flip side, he’s cozied up to dictators, taken the word of Vladimir Putin over his own intelligence agencies, shrugged off Saudi Arabia’s murder of a U.S. resident, and spilled classified information to Russians in the Oval Office. And according to a whistle-blower complaint that the administration is trying to keep secret, the president recently made a “promise” to a foreign leader that was so disturbing it prompted the filing of a formal complaint with the inspector general for the intelligence community.

The Washington Post reports that the complaint, filed by an intelligence official on August 12, was determined by IG Michael Atkinson to be credible and “troubling enough” to be deemed a matter of “urgent concern,” a legal threshold that requires notifying congressional oversight committees of its contents. (According to the New York Times, the complaint was “related to multiple acts” by Trump that went “beyond any single discussion with a foreign leader.”) But Joseph Maguire, the acting director of national intelligence who took over after Dan Coats resigned, has stonewalled Congress, declining to share the details of the president’s alleged wrongdoing with lawmakers. That decision has, unsurprisingly, enraged House Intelligence Committee chairman Adam Schiff, who issued a subpoena for the information, which Maguire has refused to comply with. On Thursday the acting director is scheduled to appear before the Intelligence committee in a classified session that is closed to the public.

According to the Post, it’s not clear which foreign leader Trump made the offer to, and considering his affection for Kim Jong Un, Mohammed bin Salman, and Putin, among others, it could truly be anyone. But, there are some potential clues: