Don't read any of David Horotwitz's books—like <em>Radicals: Portraits of a Destructive Passion</em>—if you have a light stomach for left-wing corruption. The pool of radicals, communist holdovers, and identity politics militants in the mainstream of the Democratic Party and the political left is nothing short of terrifying.
Thomas Sowell's <em>Dismantling America: and other controversial essays</em> is another great starting point.