Where an appellate court decides that circuit precedent precludes the use of a Brady violation to challenge the voluntariness of a guilty plea, does the denial of a Certificate of Appealability constitute an adjudication on the merits?

QUESTION PRESENTED 1. Where an appellate court, in connection with an application for a Certificate of Appealability ("COA"), decides that circuit precedent precludes the use of a Brady v. Maryland violation occurring prior to a guilty plea to challenge the voluntariness of the plea, does the denial of a COA based on that determination constitute an adjudication on the merits, contrary to the requirements of 28 U.S.C. § 2253 and Miller-El?