The answer shines through the next sentence in Brennan's threatening tweet: "You may scapegoat Andy McCabe [former FBI Deputy Director fired Friday night] but you will not destroy America…America will triumph over you."
It is easy to see why Brennan lost it. The Attorney General fired McCabe, denying him full retirement benefits, because McCabe "had made an unauthorized disclosure to the news media and lacked candor – including under oath – on multiple occasions." There but for the grace of God go I, Brennan must have thought, whose stock in trade has been unauthorized disclosures.
In fact, Brennan can take but small, short-lived consolation in the fact that he succeeded in leaving with a full government pension. His own unauthorized disclosures and leaks probably dwarf in number, importance, and sensitivity those of McCabe. And many of those leaks appear to have been based on sensitive intercepted conversations from which the names of American citizens were unmasked for political purposes. Not to mention the leaks of faux intelligence like that contained in the dubious "dossier" cobbled together for the Democrats by British ex-spy Christopher Steele.