Listen to the podcast "Taunting FBI leaders after firing them is not advisable" from the March 17, 2018 episode of the show
I'm no lawyer, but I don't think you have to be one to think that the President might have been doing something strongly against his own best interests when he tweeted out this attack on an outgoing FBI leader. It doesn't seem wise for a President under investigation to mock people like Andrew McCabe and James Comey, no matter how he thinks he's being treated. Let justice run its course, trust the process (and most of all its dependence on evidence), and keep petty insults to yourself. Nothing about this statement makes the President look more innocent.