Two recent examples come to mind:
- Not enforcing the company mandate of the Affordable Care Act (a.k.a. Obamacare)
- Not enforcing existing immigration laws
I'm sure there are other examples from history (and would be interested to hear them), but what legal basis does a President (and the administration) have for not enforcing existing laws?
Note: I am not asking about a decision to not defend an existing law (e.g., DOMA), but specifically about not enforcing existing law.