Andrew McCarthy reports at PJ Media,
On Tuesday, John Kelly, President Trump’s secretary of Homeland Security, published a six-page, single-spaced memorandum detailing new guidance on immigration enforcement. Thereupon, I spent about 1,500 words summarizing the guidance in a column at National Review. Brevity being the soul of wit, both the memo and my description of it could have been reduced to a single, easy-to-remember sentence:
Henceforth, the United States shall be governed by the laws of the United States.
That it was necessary for Secretary Kelly to say more than this — and, sadly, that such alarm has greeted a memo that merely announces the return of the rule of law in immigration enforcement — owes to the Obama administration abuses of three legal doctrines: prosecutorial discretion, preemption, and separation of powers (specifically, the executive usurpation of legislative power).
McCarthy explains the ways Obama abused those doctrines here.