Constitutional law doesn't mean anything when the authorities don't respect it. Constitutional law won't stop you from being arrested or killed if you don't fully submit to an authoritarian government.
There were laws in Germany to prevent what Hitler did. It still happened.
Depends what you mean by "the authorities." It's a demonstrable fact there are many small local PDs that don't give a shit about the first, fourth, or fifth amendments to name a few. That doesn't mean the Constitution "doesn't mean anything" in those places.
There were laws in Germany to prevent what Hitler did. It still happened.