If she is unable to faithfully discharge her duty to execute U.S. law, she should resign. She offers no argument to support her claim that the order was not lawful, other than her self-evident personal disagreement.
Do you know of a credible legal argument that the president is not allowed to issue instructions to the Department of Homeland Security via executive order? Ms. Yates apparently does, but she doesn't wish to share. If there is such an argument, why would it apply to President Trump's EO tightening immigration enforcement but not President Obama's EOs loosening it?
There is nothing in Trump's EO that singles anyone out by religious affiliation or background. The EO uses a list of countries that the previous administration had already highlighted as high-risk. The EO imposes a temporary ban only, for the explicit purpose of reviewing the processes used to grant visas to nationals of those high-risk countries. I'm really not seeing anything blatantly improper or illegal here.
Where does the chief law enforcement officer's obligation to enforce the law as enacted by the people of the United States cave to his/her personal proclivities or opinions about that law? It is the duty of the AG to execute the laws as written. If we allow the AG to ignore the laws we set up based on matters of personal opinion, isn't that a large subversion of the democratic process?
Principled stands like this should truly be exceptional, and clearly and obviously justified. If you're getting into minutia about whether something may or may not be legal, we've set up a system of judges whose role is to make these decisions. In the meantime, it is the DoJ's duty to enforce the law.
Prosecutorial discretion refers specifically to prosecuting someone under the law. It does not apply to the government's own lawyers refusing to advocate for or defend the government's position in hearings about the very legality of the Orders issued -- this leaves the administration without fair representation and stands only to prolong the litigation process.
If Ms. Yates could not in good conscience fulfill the duties of her position, the appropriate course of action is resignation. If she refuses to take this course, it is the president's responsibility to relieve her and install someone who is willing to uphold the laws that the people of the United States have installed through their duly elected representatives and executives (including the president).