courts addressing § 2423(b) have relied on longstanding case law interpreting the Mann Act's use of the statutory phrase. See, e.g., United States'. Garcia-M, 234 F.3d 217, 220 n.3 (5th Cir. 2000); United States I. Yang, 128 F.3d 1065, 1069-70 (7th Cir. 1997); United Statosi. Ellis 935 F.2d 385, 389-90