Whether a 28 U.S.C. § 2255 petitioner alleging ineffective assistance of counsel for failing to object to a Government's Due Process-violating breach of a proffer agreement satisfies the 'substantial showing' standard for a Certificate of Appealability (COA)

1. Whether a 28 U.S.C. § 2255 petitioner who alleges constitutionally ineffective assistance of counsel for faling to object to the Government's Due Process-violating breach of a proffer agreement at sentencing satisfies the "substantial showing" standard for a Certificate of Appealability (COA) under Slack v. McDaniel , 529 U.S. 473 (2000). 2. Whether a court of appeals may impose a jurisdictional or procedural bar, -contrary to the remedial, purpose of § 2253(c)(2) and the mandate of Miller-EL v. Cockrell , 537 U.S. 322 (2003), to deny a COA on the basis that a claim of procedural error such as the denial ofan evidentiary hearing was first articulated in the COA pleadings . ii