The president’s serial violations of that charge undermine the balance of our system. The essence of legislative power, according to Federalist 78, is “will.” That is, in our republic, it is the duty of the Congress to direct our political course, within the boundaries set by the Constitution (and the law of nature). However, when the president only follows the laws he likes–and the parts of the laws he likes–his becomes the ultimate will in the system.
When “will” and “force” (the primary executive power) combine, they pose a special menace to liberty. Legislative will, to be just, must be expressed in general, forward-looking laws. Thus the Constitution explicitly prohibits both ex post facto (retroactive) laws and bills of attainder (which declare a given party guilty of a crime without trial–with penalty attached). Executive force, to be just, must be applied against specific offenders for past actions. When the same hands exercise both powers, however, the law easily becomes an instrument of force, used to target opponents with oppressive rules that are only ex post facto laws and bills of attainder by another name.
We know, at least in part, what this looks like from the Administration’s Obamacare contraceptive rules, its IRS abuses, its recent EPA greenhouse gas rules, and more. Obama apologists might counter that what has been gained in Progressive reform outweighs any harm done to American constitutionalism.