What is the test for reversing a criminal conviction in a federal criminal case where a prosecutor made inappropriate remarks to a defendant?

Assuming those remarks were inappropriate, "[i]nappropriate prosecutorial comments, standing alone, would not justify a reviewing court to reverse a criminal conviction obtained in an otherwise fair proceeding." United States v. Young, 470 U.S. 1, 11 (1985). Reversal of a conviction due to prosecutorial misconduct is only warranted if it causes the defendant "substantial prejudice," United States v. LaMorte, 950 F.2d 80, 83 (2d Cir. 1991), that "so infected the trial with unfairness as to make the resulting conviction a denial of due process," Darden v. Wainwright, 477 U.S. 168, 181 (1986) (internal quotation marks omitted); see also United States v. Shareef, 190 F.3d 71, 78 (2d Cir. 1999). We consider the following factors in evaluating whether prosecutorial misconduct caused substantial prejudice: "(1) the severity of the alleged misconduct; (2) the curative measures taken; and (3) the likelihood of conviction absent any misconduct." United States v. Locascio, 6 F.3d 924, 945-46 (2d Cir. 1993). When a defendant fails to object to the summation at trial, we "will not reverse absent flagrant abuse." United States v. Zichettello, 208 F.3d 72, 103 (2d Cir. 2000) (internal quotation marks omitted).