Ramiro Gareia-Cardenas (Garcia) appeals his guilty-plea conviction and sentence for being found in the United States following deportation and removal, without having obtained the consent of the Attorney General or the Secretary of the Department of Homeland Security. Garcia argues that 8 U.S.C. §§ 1326(b)(1) & (b)(2) are unconstitutional and that Almendarez-Torres v. United States, 523 U.S. 224, 235, 118 S.Ct. 1219, 140 L.Ed.2d 350 (1998), should be overruled. He also contends, in light of United States v. Booker, — U.S. -, 125 S.Ct. 738, 160 L.Ed.2d 621 (2005), that the district court plainly erred in sentencing him because the court believed that the Federal Sentencing Guidelines were mandatory, rather than advisory.

Because Garcia raises these issues for the first time on appeal, we review only for plain error. See United States v. Mares, 402 F.3d 511, 513 (5th Cir. 2005), petition for cert. filed, No. 04-9517, — U.S. -, — S.Ct. -, — L.Ed.2d - (U.S. Mar. 31, 2005). Although the decision in Almendarez-Torres has been called into question, see Shepard v. United States,U.S. -, -, 125 S.Ct. 1254, 1264, 161 L.Ed.2d 205 (2005) (Thomas, J., concurring), the Supreme Court has not overruled it. Accordingly, Garcia’s first argument is foreclosed. See United States v. Rivera, 265 F.3d 310, 312 (5th Cir. 2001).

Garcia’s assertion that prejudice should be presumed from the sentencing court’s Booker error is without merit. See Mares, 402 F.3d 511, 520-522. Garcia is not challenging the calculation of his criminal history score or the characterization of his prior conviction as an aggravated felony. Although Garcia argues that there is a reasonable probability that he would have received a lower sentence under an advisory guidelines scheme, he concedes that “[i]t is impossible to know for certain what the judge might have done if freed of the constraints of the mandatory Guidelines.” Under Mares, this is insufficient to establish that the error affected his substantial rights. Mares, 402 F.3d at 522. Accordingly, Garcia has not established plain error with respect to his sentence.

AFFIRMED.