Whether a state attorney general has a duty to defend the validity of state law is a complicated question, one that cannot be decided by reference either to the oath state officers must take to support the federal Constitution or the supremacy of federal law. Instead, whether a state attorney general must defend state law turns on her own state’s laws. Each state has its own constitution, statutes, bar rules, and traditions, and not surprisingly, the duties of attorneys general vary across the states. To simplify somewhat, we believe that there are three types of duties. One set of attorneys general has a duty to defend state law against state and federal challenges, while a second group has no duty to defend state law in such scenarios. A third cohort of attorneys general has a power (and in some cases a duty) to attack state statutes of dubious validity. They may (or must) proactively file suit to obtain judicial resolution of constitutional questions. Given that these duties vary across the states, politicians (including attorneys general) who blithely conclude that all state attorneys general must defend all state laws or, conversely, that all may refuse to defend whenever they believe a state law is unconstitutional evince a lamentable indifference to the power of states to craft an office that suits their particular needs. As the same-sex marriage debate reveals, categorical statements about whether state attorneys general must (or must not) defend bars on same-sex marriage are usually little more than self-serving sound bites from elected, politically ambitious attorneys general, intended for constituents focused on policy outcomes rather than legal questions. With Democrats and Republicans squarely divided on issues like same-sex marriage, gun control, and campaign finance, we predict that attorneys general will increasingly seek political advantage by refusing to defend (or insisting on the defense of) laws that divide the parties. We also foresee that failures to defend will be especially likely to occur in states where the attorney general is of a different political party than the governor, legislature, or the preceding attorney general.

Citation
Neal Devins & Saikrishna Prakash, Fifty States, Fifty Attorneys General, and Fifty Approaches to the Duty to Defend, 124 Yale Law Journal, 2100–2187 (2015).
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