Clark was visit- ing the United States-and the commercial sex act did not occur until June 2003. Mere sil "ignorance of the law will not excuse." Shevlin-Carpenter Co. Minn., 218 U.S. 57, 68, 30 S.Ct. 663, Ltd. 930 (1910). Clark might have been ignorant of the law, but he had constitutionally sufficient no- tic