Doing so suggests the president knew at the time that Flynn had done something that is against the law, and therefore the investigation could not be as frivolous as he's been portraying.

It's also unclear how he would know that, if information about Russian contacts had not reached him, as he has been implying in his own defense.

Flynn left the White House in February, only acknowledging that he had given an incomplete account to Pence of his conversations with Russian Ambassador Sergey Kislyak. After Trump forced Flynn out, he asked FBI Director James Comey to end the bureau's probe in the matter, according to Comey's account. Comey refused, and Trump fired him, too.