[F]ollowing our decision in Erie R. Co. v. Tompkins, 304 U.S. 64 [] (1938), federal courts are generally no longer permitted to promulgate new federal common law causes of action . . . .[1]

When a party seeks to assert an implied cause of action under the Constitution itself . . . separation-of-powers principles are or should be central to the analysis. The question is 'who should decide' whether to provide for a damages remedy, Congress or the courts?[2]

In the scheme of the Constitution, [state courts] are the primary guarantors of constitutional rights, and in many cases they may be the ultimate ones. If they were to fail, and if Congress had taken away the Supreme Court's appellate jurisdiction and been upheld in doing so, then we really would be sunk.[3]