Well it usually doesn't come up because Presidents by and large don't try to do things that aren't constitutional.
Really? I'm not a constitution specialist so I could be wrong here in which case please correct me but...
Was Hiroshima and Nagasaki's atomic bomb cowardly dropped on civilians, constitutional? Don't remember any judge trying to stop that or impeaching Truman for such a horrible act.
Was the creation of the FED which is basically a private organization running and printing dollars with the blessing of whatever president was in charge at the time, a constitutional thing?
Is the NSA and CIA spying on private communications (as Snowden proved to the world) of pretty much every citizen in the world a constitutional thing?
I could go on for a while if I wanted but these few example will do. The point being that the forces in power seem to worry about the constitution when it suits them and when it does not, they seem to be using the constitution as toilet paper.