The United States Supreme Court has held that federal courts must abstain from intervention into pending state proceedings under the Younger doctrine when the federal plaintiff has an available state court opportunity to raise his federal constitutional claim.
Moore v. Sims, 99 S. Ct. 2371 (1979)
David C. Levenreich,
Constitutional Law - Civil Rights Action - Federal Court Review of State Statutes - Abstention,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol18/iss3/12