There are questions as to whether he did or not back in the 70's when he was discharged from the Navy
The only way to find out for sure is for Kerry to sign the 180 form
He REFUSES to do so
Kerry received an HD because the Navy never prosecuted him for the "crime," i.e., meeting with the enemy in time of war. Yanking his security clearance would not prevent him from getting an HD. Senators still need a security clearance. If I recall, Leahy was kicked off of the intelligence committee for leaking information.