Subject: Re: Another Win For President Trump
In your example, the theoretical candidate violated a federal law with the fact determiner ultimately being a federal agency (meaning, there's no crime unless the IRS testifies that so-and-so hasn't filed a return).

Not at all. The IRS isn't the finder of fact - the court is. If the plaintiffs can prove their case without IRS testimony, then IRS participation isn't necessary.

I run into this all the time in the environmental permitting side of my practice. A lot of state environmental laws will incorporate by reference the federal standards for whatever the subject matter is (wetlands permitting, pollution control, what have you). So the state and local agencies will make a determination whether those standards have been met. It's really not all that unusual for state courts to apply federal law (or vice versa) when circumstances require it.