Lawrence Tribe, constitutional law professor at Harvard said something interesting: By claiming Comey had told him that the FBI wasn’t investigating him, Trump waived executive privilege with regard to Trump/Comey exchanges.
Samuel Buell, law professor at Duke (and former federal prosecutor), said that while it’s ambiguous at the moment if firing Comey qualifies as obstruction of justice, threatening him later on Twitter makes the case for obstruction much clearer.
So basically: All the levers of power are Trump’s to lose, so keep tweeting!
Funny, because Comey probably waived his legal rights too, by discussing them openly as well. Weird, I know, a horse a piece. He said, she said … not a lot to go on there.