United States citizenship of the respondent can be raised as a defense to removal. Murphy v. INS, 54 F.3d 605, 610 (9th Cir. 1995). The government bears the heavy burden of proving alienage through "clear, unequivocal, and convincing evidence."  Scales v. INS, 232 F.3d 1159, 1163 (9th Cir. 2000) (quoting Woodby v. INS, 385 U.S. 276, 277 (1966)); see also Lopez-Urenda v. Ashcroft, 345 F.3d 788, 795 (9th Cir. 2003) (citations omitted); 8 U.S.C. 1229a(c)(3)(A).  As the Ninth Circuit has explained, "[t]his burden of proof is much more than a mere preponderance of the evidence.  The evidence must not leave the issue in doubt."  Lim v. Mitchell, 431 F.2d 197, 199 (1970) (citation omitted); see also Murphy v. INS, 54 F.3d 605, 610 (9th Cir. 1995) (noting that the clear and convincing evidence standard is a "heavier burden than the preponderance of the evidence standard") (citation omitted).      Because a United States citizen cannot be removed from the country, reliable proof of alienage in a removal proceeding is constitutionally required.  As the Supreme Court has long recognized, "[t]o deport one who . . . claims to be a citizen[ ] obviously deprives him of liberty, . . . [and] may result also in loss of both property and life; or of all that makes life worth living."  Agosto v. INS, 436 U.S. 748, 753 (1978) (quoting Ng Fung Ho v. White, 259 U.S. 276, 284 (1922)); cf. Bridges v. Wixon, 326 U.S. 135, 154 (1945) ("[D]eportation . . . visits a great hardship on the individual and deprives him of the right to stay and live and work in this land of freedom. . . . Meticulous care must be exercised lest the procedure by which he is deprived of that liberty not meet the essential standards of fairness."). Thanks to Jennifer C. Chang for this argument.