They’ll squash state resistance AND it’ll be deemed illegal.

2. State Self-Help. - Even if national political safeguards of state interests in foreign relations do not eclipse the new federalism, another political alternative - state self-help - may. States may, for example, adopt legislation or conduct activities in such a way as to diminish the need for federal intervention and, accordingly, for reliance on their constitutional immunities. But wholesale displacement is relatively rare. Such activities may also deter federal intervention by raising its political costs, but here too the effect is probably marginal and potentially even negative (state activities may, after all, inspire preemption), and the courts may nonetheless read state authority narrowly.

More dramatically, state conducted foreign relations might undermine the perceived federal monopoly on foreign affairs: to the extent that such activities create new sovereign identities, while avoiding the problems associated with state interference, they arguably undermine the justifications for federal exclusivity and for plenary federal power. If so, the treaty power might wither of its own accord, irrespective of whether states had more specific doctrinal defenses that they could assert. Alternatively, state activities might indirectly contribute to those defenses by decreasing the functional argument for preserving an unfettered treaty power.

As I have argued elsewhere, though, existing state foreign relations activities have nothing like this kind of transformational character. Their uncertain constitutional status probably retards their growth, and the Supreme Court has been slow to clarify matters. In the interim, national governments still dominate international relations, and to the extent the states participate, foreign governments scarcely hold the United States harmless. Where the situation warrants national intervention, the federal government possesses a number of tools that are reasonably adequate to exterminate divisive or disruptive state activities - including not only the treaty power, but also the power to regulate foreign commerce. Even if those tools do not necessarily allow the federal government to achieve its aims in international affairs, their continued presence dampens any prospect for a state-induced revolution in foreign relations authority.