From the summary of the decision in Minnesota RFL Caucus v. Freeman:

The relevant section of the Minnesota Fair Campaign Practices Act – Minn. Stat. Sec. 211B.02 – prohibits a candidate from falsely stating that a candidate or ballot question has the support or endorsement of a major political party; the statute further provides that county attorneys may prosecute violations of the statute. Plaintiffs contend the statute violates their First Amendment rights, and they sued four Minnesota county attorneys with authority to criminally prosecute violations and asked the district court for a preliminary injunction to prohibit the county attorneys from enforcing the statute pending disposition of the case; the district court denied their motion, and plaintiffs appeal the denial of the preliminary-injunction motion. The district court did not err in denying the motion as the defendants had not enforced the statute and have not threatened to do so and were entitled to Eleventh Amendment immunity.

Plaintiffs brought a challenge alleging a First Amendment violation. But the evidence showed that the county attorneys testified “that they never have initiated civil or criminal proceedings for violations of § 211B.02, that they are ‘not currently investigating’ any such violations, and that they have ‘no personal intention’ to commence proceedings.” That was enough for the Eighth Circuit to conclude that a preliminary injunction was inappropriate. The court holds that Ex parte Young offers an independent barrier to plaintiffs seeking relief, beyond a claim where a plaintiff has standing and a claim is ripe for judicial review: those cases in which an official “has neither enforced nor threatened to enforce the statute challenged as unconstitutional.”