This single act is enough evidence for the removal of Brennan's security clearances:

On August 25,  2016,  three months before Trump's Inauguration,  CIA Chief,  John Brennan,  briefed Harry Reid as to the contents of the Steele Dossier which wound up in a letter from Reid  to the FBI,  which, in turn, was used as a predicate for the first FISA Court warrant to spy on the Trump Campaign   . . . .  justification enough  . . . . 
reason for ending his security clearances.

More than this,  Brennan continues to label Trump a "subversive,"  accusing him of treason,  and,   defending that position.   The man needs security clearance like he needs another mouth.  

Now you know.