Can federal courts second-guess a State's 'reason' for exercising Tenth Amendment authority?

Under Missouri law, state officials cannot use state resources to enforce certain federal laws. In response to a suit filed by the Federal Government challenging this law, the Eighth Circuit agreed Missouri has core Tenth Amendment authority to pass such a law. The court nonethel ess struck down Missouri’s law on the grou nd that Missouri’s legislature enacted it for a forbidden “reason ”—the legislature’s belief that certain federal laws are unconstitutional. The questions presented are : 1. Can federal courts second -guess a State’s “reason” for exercising Tenth Amendment a uthority (as the Eighth Circuit held ) or not (as other circuits hold )? 2. Does the Constitution prohibit States from exercising Tenth Amendment authority when motivated by a concern that a federal statute is unconstitutional? 3. Is a state official a proper defendant under Ex parte Young simply because the official is regulated by a statute (as the Eighth Circuit held ), or does the official also need to possess authority to enforce the law (as other circuits hold )?