Johnsen considers the legitimacy of what he terms "presidential non-enforcement," that is, whether and when the President may disobey an unambiguous congressional command enacted in conformity with the constitutionally prescribed lawmaking process on the ground that the President believes the law is unconstitutional.
Dawn E. Johnsen,
Presidential Non-Enforcement of Constitutionally Objectionable Statutes,
63 Law and Contemporary Problems
Available at: http://scholarship.law.duke.edu/lcp/vol63/iss1/2