The mechanism is checks and balances. In other words the officers of the other branches interpreting and implementing the Constitution, instead of kowtowing to what the founders intended to be the weakest branch.
Well, the essential question of what comports with the Constitution got put on the back of the USSC, for lack of a different body or mechanism. To let the executive and legislature be on their honor for that might be an equally vexing problem down the road.
This is one of the things that the Bork Amendment has been proposed to get around.