hancements would be applied. [3][4] Issues regarding the interpretation and en- forcement of a plea agreement are reviewed de novo. United States' Martinez-Noriega, 418 F.3d 809, 811 (8th Cir.2005); United States' DeWitt, 366 F.3d 667, 669 (8th Cir.2004). "Plea agreements are contractual in nature, and should