Three key campaign-finance challenges, one already at the U.S. Supreme Court, seek to push through doors left open by the justices’ controversial Citizens United decision.

Advocates and opponents of campaign-finance regulations are watching, in particular, U.S. v. Danielczyk, now being briefed in the U.S. Court of Appeals for the 4th Circuit. The government is appealing a district court ruling that struck down the federal ban on direct corporate contributions to candidates.