Can a prosecutor's misconduct in a criminal proceeding be grounds for a writ of habeas corpus?

Prosecutorial misconduct in a state criminal proceeding will be grounds for a writ of habeas corpus unless the prosecution can show that the error was harmless beyond a reasonable doubt. Chapman v. California, 386 U.S. 18, 24, 87 S.Ct. 824, 828, 17 L.Ed.2d 705 (1967). The question of whether respondents have proved harmlessness beyond a reasonable doubt is a mixed question of law and fact which should be reviewed de novo since it does not call for a predominantly factual inquiry. United States v. McConney, 728 F.2d 1195, 1204 (9th Cir.), cert. denied 469 U.S. 824, 105 S.Ct. 101, 83 L.Ed.2d 46 (1984).