In a police state, almost any sort of behavior can be compelled for any amount of time. You underestimate the moral corruption of those with power and vastly overestimate the value of the US constitution. Hint: The US has been operating an extra-legal KZ for quite some time now. They could not do that if the US constitution had any value.
So just threaten said employees with life in prison for exposing "secrets critical to national security" and you are done.
But why bother with the charade? In other police states, people disappear with no reason. There is no secret court. There is no "process". They just do what needs to be done. Opposition politicians, investigative journalists, enemies of those in power, and, in many cases, friends of those in power are arrested one day and never heard from again. That hasn't been happening. Stupid cowboy shit like bugging the phones of world leaders, yes. Compelling the secrecy of secret surveillance, yes. But as far as I know, the Feds aren't shredding the Bill of Rights (outside of airports, but that's a special case of its own--you can fly anywhere without being searched, just not on a major carrier).
So are we at the end of a 12-year transitional period that spans two administrations? OR is all of this cloak and dagger stuff considered genuinely necessary by a law enforcement apparatus that really really wants to operate legally but feels that tipping off criminals will make them impossible to catch?
Gag orders are as undemocratic as it gets, and way too blunt an instrument for a society that can and should have come up with a more refined successor to the PATRIOT Act by now. But there isn't anything reported so far that is inconsistent with the law -as written-. Declaring the Constitution null and void based on the actions of the NSA and FBI to "Intercept and Obstruct Terrorism" is a bit premature, given that they are doing so with the blessing of Congress.