I believe that everyone who leaves the employment of the federal government should have their security clearances revoked immediately. If they come back then a new background or updated one should be conducted.
This would dlow down the revolving door of government employees going to private sector then back to government.
People like Brennan , clapper and the like should all loose their clearances.
All federal agents who leave the agencies should have their clearances revoked. You should only be able to get a clearance if you are actually employed by the government.