Gertsenshteyn v. Mukasey, 544 F.3d 137 (2d Cir. Sept. 25, 2008) ("When the Government has decided to seek the removal of a lawfully admitted alien under 8 U.S.C. 1227(a)(2)(A)(iii), the Government is obligated to prove that the alien's conviction falls within the statutory definition of "aggravated felony." See 8 U.S.C. 1229a(c)(3)(A); Ibragimov v. Gonzales, 476 F.3d 125, 131 (2d Cir .2007). That the Government finds that task difficult in some cases is no reason for immigration courts to renounce the restrictions that the courts have said the law requires.")