We review de novo the district court's application and interpretation of the United States Sentencing Guidelines. 18 U.S.C. § 3742(e); United States v. Domino, 62 F.3d 716, 719 (5th Cir. 1995) (footnote and internal citations omitted). Calculations under the guidelines begin with the determination of the appropriate base offense level for each count of conviction.

ANALYSIS We review the district court's application and legal interpretation of the sentencing guidelines de novo, United States v. Domino, 62 F.3d 716, 719 (5th Cir. 1995), and its findings of fact for clear error. United States v. Hooker, 997 F.2d 67, 75 (5th Cir. 1993).

The Supreme Court's decision Peugh v. United States , 569 U.S. 530, 133 S.Ct. 2072, 2082–84, 186 L.Ed.2d 84 (2013), establishes that where the wrong Guidelines are consulted and those Guidelines expose a defendant to greater punishment, the district court violates the Ex Post Facto Clause. Id. at 2084 ("A retrospective increase in the Guidelines range applicable to a defendant creates a sufficient risk of a higher sentence to constitute an ex post facto violation."); see also, e.g., United States v. Armstead , 114 F.3d 504, 510 (5th Cir. 1997) ("A sentence that is increased pursuant to an amendment to the guidelines effective after the offense was committed violates the ex post facto clause.") (quoting United States v. Domino , 62 F.3d 716, 720 (5th Cir. 1995) ). Cf. United States v. Shakbazyan , 841 F.3d 286 (5th Cir. 2016) (clarifying that Peugh will not save a defendant who commits one of the alleged crimes after the effective date of the Guidelines in question).

As a general rule, if the text of the stipulation and inferences that may be drawn from the record demonstrate a "clear waiver" or "intentional by-passing of an opportunity to assert a known right," then a subsequent attack on the prior conviction is barred.See United States v. Domino, 62 F.3d 716, 719 (5th Cir. 1995).Mitchell v. United States, 482 F.2d 289, 292 (5th Cir. 1973).

Both the PSR and the district court used the 2002 Guidelines to calculate Duhon's sentencing range because the newer Guidelines in effect at the time of Duhon's sentencing were less favorable to him. See United States v. Domino, 62 F.3d 716, 720 (5th Cir. 1995). Duhon objected to the PSR's suggested enhancements for the age of the children and number of images involved, citing Blakely v. Washington, 542 U.S. 296, 124 S.Ct. 2531, 159 L.Ed.2d 403 (2004).

The guidelines in effect on the date a defendant is sentenced apply "unless the court determines that `use of the Guidelines Manual in effect on the date that the defendant is sentenced would violate the ex post facto clause of the United States Constitution,' in which case the court should use the version of the guidelines in effect on the date that the offense of conviction was committed." United States v. Domino, 62 F.3d 716, 719-720 (5th Cir. 1995) (quoting U.S.S.G. § 1B1.11). Because the court sentenced Calderon-Pena after the effective date of the 2001 guidelines, those guidelines should be used unless doing so results in a harsher sentence than would be given under the 2000 guidelines.

United States v. Braxton, 903 F.2d 292 (4th Cir. 1990), reversed on other grounds, 500 U.S. 344 (1991), understands "stipulation" in this way, and we think correctly so. Defendants' protection against undue severity lies not in reading "stipulation" as requiring a formal agreement (under seal, perhaps?) but in taking seriously the requirement that the basis of the more serious offense be established "specifically". See United States v. Domino, 62 F.3d 716, 720-22 (5th Cir. 1995). That was accomplished here, and the district judge therefore properly applied sec. 2D1.10.

We review de novo a determination of the meaning and effect of any factual stipulations on a sentence. See Braxton v. United States, 500 U.S. 344, 350, 111 S.Ct. 1854, 114 L.Ed.2d 385 (1991); United States v. Domino, 62 F.3d 716, 719 (5th Cir. 1995). We also give plenary review to the decision concerning which guideline provision is most analogous to the offense of conviction.

Cir. 1991) (requiring a "knowing agreement by the defendant, as part of a plea bargain, that facts supporting a more serious offense occurred and could be presented to the court" for the court to apply section 1B1.2(a)); United States v. McCall, 915 F.2d 811, 816 n. 4 (2d Cir. 1990) (requiring that any stipulation be part of the plea agreement itself); United States v. Rutter, 897 F.2d 1558, 1561 (10th Cir. 1990) (explaining that once the government agrees to a plea bargain without extracting an admission, facts admitted by the defendant can be considered only as relevant conduct in determining the appropriate guideline range, not as stipulations under section 1B1.2(a)). But see United States v. Loos, 165 F.3d 504, 508 (7th Cir. 1998) (concluding that the objective behind section 1B1.2(a) is best achieved by reading "stipulation" to mean any acknowledgment by the defendant that he committed the acts that justify use of the more serious guideline), cert. denied, 119 S.Ct. 1090 (1999); United States v. Domino, 62 F.3d 716, 722 (5th Cir. 1995) (assuming that the factual resume — the equivalent of the "factual basis" in this case — can contain stipulations). In this case, where the parties drafted and agreed to a document that explicitly contained all of the relevant stipulations between them, it is clear that their "deal" encompassed only those stipulations contained in that document.

Mankins misconstrues, however, the required proof of the underlying offense and, thus, the nature of a § 843(b) violation. United States v. Domino, 62 F.3d 716 (5th Cir. 1995); United States v. Martinez, 950 F.2d 222 (5th Cir. 1991). A conviction under § 843(b) requires proof that a defendant (1) knowingly or intentionally (2) used a communications facility (3) to facilitate the commission of a drug offense.