Former four-star general speculates whistleblower scandal could involve Trump giving Putin an American
US president Donald Trump and Russian president Vladimir Putin met for face-to-face talks in Osaka on Friday. (AFP)

It remains unclear exactly what were the issues cited by the whistleblower who expressed concern at actions of President Donald Trump as a threat to national security, at least one of which involved a promise the president allegedly made in a phone call with a foreign leader.

But former Gen. Barry McCaffrey had a chilling thought about what it could possibly be — and posted his speculation on Twitter: