separation of powers

is important because human frailty suggest that it would too big a temptation for self-exemption for the same persons who have the power of making laws, to have also in their hands the power to execute them.

And because it may be too great a temptation to human frailty, apt to grasp at power, for the same persons, who have the power of making laws, to have also in their hands the power to execute them, whereby they may exempt themselves from obedience to the laws they make, and suit the law, both in its making, and execution, to their own private advantage. John Locke

is violated when Congress exonerates itself from the impositions of the laws it obligates people outside the legislature to obey.

One might plausibly contend that Congress violates the spirit, if not the letter, of the constitutional doctrine of separation of powers when it exonerates itself from the impositions of the laws it obligates people outside the legislature to obey.

separation of powers, n.All

separation of powers