Justin Levitt has a post with this title at Election Law Blog, with an overview and links to coverage. The decision happened yesterday, in United States v. Danielczyk. (See here for my oral argument preview and a link to AP coverage of the oral argument itself.)
Judge Gregory wrote the opinion, which was joined in by Chief Judge Traxler and Judge Diaz. This opinion must have brought Judge Gregory some satisfaction. The controlling Supreme Court decision, FEC v. Beaumont, came to the Supreme Court out of the Fourth Circuit. Judge Gregory authored a panel dissent in that case, and the outcome he advocated in dissent was adopted by the Supreme Court.