Evidently the courts, by their own traditions and actions, see themselves as law givers and enforcers. They usurp that authority by acquiescence of the other branches.
Exactly so, Alamo-Girl. The Framers created a public order out of three branches, and they expected those three branches would from time to time be in dynamic conflict with each other, in the struggle to preserve the powers and privileges the Constitution vests in each. If somebody in one branch were to exceed his mandate, then one or both of the other two branches would be expected to "do his duty" and put the miscreant in his place.
The Constitution is premised in a dynamic process of creative conflict.