At Josh Blackman's Blog, The Text of the “Take Care” Clause. Key conclusion:
With this selection of “faithful” [in the take care clause], the framers adopted a standard well known in the common law of contracts—one of good faith. The Constitution did not include language such as “shall think proper,” which would suggest a subjective good faith standard, based on how the President envisages his own independent duty to execute the law. Rather, the duty was pegged to the “Laws” of Congress, preferring an objective good faith standard based on what Congress would want the President to do in such a situation.
In this sense, akin to the law of agency, the President serves as a “faithful” agent to Congress, and to the people, the ultimate sovereigns, and residual of all legitimate governance. The people elect Congress to write the laws, and choose the President to enforce the laws on their behalf. Viewed this way, the Take Care clause is indeed the fulcrum that holds together our entire system of governance. The President always has an independent constitutional duty to not obey unconstitutional laws. But he must remain a faithful steward of the laws of Congress, and cannot shirk that duty when he disagrees with them.
Due to the unavoidable dilemma of inadequate resources, even in good faith, the President will not be able to enforce all of the laws. Within that framework, the President can decide to allocate priorities. However, deliberately declining to enforce the laws, as a means to bypass laws the Executive dislikes, and Congress will not change, is not in good faith. To ascertain the state-of-mind of the President, the “sole organ” of the Executive branch, a careful study should be made of all official, and unofficial administration statements, particularly if they are against interest. If a pattern of behavior reveals a deliberate effort to act not in good faith, but in an effort to sabotage or undermine the Laws of Congress, the duty under Article II has been violated. Here, the President has dislodged Article II’s fulcrum, knocking out of orbit this fixed star in our constitutional constellation.