If the client is a United States citizen, no ground of deportation can be applied.  A person can acquire United States citizenship in several ways:

SAFE HAVENS - GENERAL SAFE HAVENS - CONVICTION-BASED GROUNDS OF DEPORTATION
Costello v. INS, 376 U.S. 120 (1964) (person who was convicted of two crimes involving moral turpitude while he was a United States citizen cannot be deported on account of them after he lost his citizenship through denaturalization).

BIA

APPLICANT FOR ADMISSION - BURDEN OF PROVING CITIZENSHIP
An applicant for admission to the United States as a citizen of the United States has the burden of proving citizenship. Matter of GR, 3 I. & N. Dec. 141 (BIA 1948). Once the applicant establishes that s/he was once a citizen and the government asserts that s/he lost that status, then the government bears the burden of proving expatriation. Ibid. The standard of proof to establish expatriation is less than the clear and convincing evidence test as applied in denaturalization cases, but more than a mere preponderance of evidence. The proof must be strict and exact. Ibid.

First Circuit

CITIZENSHIP - DERIVATIVE CITIZENSHIP ILLEGAL REENTRY - CITIZENSHIP - EXCLUSION OF EVIDENCE
United States v. Guerrier, 428 F.3d 76 (1st Cir. Nov. 8, 2005) (defendant's claims of error in both the exclusion of evidence regarding his claim of derivative United States citizenship and an improper sentence enhancement as a result of his prior convictions were without merit).
http://laws.lp.findlaw.com/1st/041749.html

Second Circuit

CITIZENSHIP - ACQUIRED CITIZENSHIP - BIOLOGICAL PARENTAGE IS NECESSARY TO A CLAIM TO UNITED STATES CITIZENSHIP UNDER FORMER INA 301(a)(3)
Colaianni v. INS, 490 F.3d 185 (2d Cir. Jun. 15, 2007) (per curiam) (petition for review denied on basis that noncitizen's claim to be United States citizen, advanced as a defense in removal proceedings, was invalid, since biological parentage is necessary for a person to claim citizenship under former INA 301(a)(3) because of the plain language of the statute, which refers to persons "born ... of parents both of whom are citizens of the United States" and pertains only to the acquisition of citizenship "at birth."), citing Marquez-Marquez v. Gonzales, 455 F.3d 548, 556-57 (5th Cir.2006) (rejecting the same argument based upon a plain reading of the statute).

Third Circuit

CITIZENSHIPDERIVATIVE CITIZENSHIP
Morgan v. Attorney General, ___ F.3d ___, 2005 WL 3481443 (3d Cir. Dec. 21, 2005) (petition for review of derivative citizenship claim under 8 U.S.C. 1432(a)(3) denied on merits, because petitioner cannot establish that her parents were legally separated at the time her mother was naturalized).

Lower Courts of Third Circuit

CITIZENSHIP - DERIVATIVE CITIZENSHIP
Kajtazi v. INS, ___ F. Supp. 3d ___, 2005 U.S. Dist. LEXIS 24173 (D.N.J. Oct. 14, 2005) (federal habeas petition granted under 28 U.S.C. 2241 challenging an INS detainer on the ground that Petitioner acquired derivative United States citizenship on July 31, 1985, when his father naturalized).

Fifth Circuit

CITIZENSHIP - BIRTH IN UNITED STATES
Lopez v. Holder, ___ F.3d ___, 2009 WL 682991 (5th Cir. Mar. 17, 2009) (without consent of petitioners, magistrate judge did not have jurisdiction to try citizenship case based on birth).

Ninth Circuit

RELIEF - NATURALIZATION
United States v. Hovsepian, 422 F.3d 883 (9th Cir. Sept. 6, 2005) (district court's decision to administer oath of citizenship affirmed where district courts finding that they were persons of good moral character was not clearly erroneous).
http://caselaw.lp.findlaw.com/data2/circs/9th/9950041p.pdf

JUDICIAL REVIEW - CITIZENSHIP
Theagene v. Gonzales, __ F.3d __, 2005 WL 1398833 (9th Cir. June 15, 2005) ("Because only an "alien" may be required to exhaust administrative remedies under 1252(d)(1), the plain language of 1252(b)(5) requires that upon a petition for review of the BIA's final order of removal, we must evaluate a petitioner's claim to United States nationality regardless of whether the claim was raised below.").

IMMIGRATION STATUS - NATIONAL OF THE UNITED STATES
United States v. Karaouni, 379 F.3d 1139, 1143 (9th Cir. Aug. 24, 2004) ("All citizens of the United States are nationals, but some nationals, such as persons born in American Samoa and other U.S. territorial possessions, are not citizens. 8 U.S.C. 1408; Perdomo-Padilla v. Ashcroft, 333 F.3d 964, 967-69 (9th Cir.2003). Indeed, the term "national of the United States" is defined as including "a person who, though not a citizen of the United States, owes permanent allegiance to the United States." 8 U.S.C. 1101(a)(22). Thus, a claim to be a U.S. national is not a claim to be a citizen, but a claim to be a member of a broader group that includes citizens as well as others.      As a legal concept, the term U.S. national came into use in the after-math of the Spanish-American War to clarify the status of persons born in the territories that the United States acquired from Spain. Hampton v. Mow Sun Wong, 426 U.S. 88, 91, 107-13, 96 S.Ct. 1895, 48 L.Ed.2d 495 (1976); Rabang v. INS, 35 F.3d 1449, 1452 (9th Cir.1994); Cabebe v. Acheson, 183 F.2d 795, 797-801 (9th Cir.1950). We recently have given the term a narrow construction, holding that an alien does not become a national simply by signing a statement of allegiance in a naturalization application, Perdomo-Padilla, 333 F.3d at 972, or by serving in the U.S. armed forces after taking the standard military oath of allegiance. Reyes-Alcaraz v. Ashcroft, 363 F.3d 937, 939-41 (9th Cir.2004).").

NATIONAL OF THE UNITED STATES - MILITARY SERVICE DURING CONFLICT INSUFFICIENT
Reyes-Alcaraz v. Ashcroft, 363 F.3d 937, 938 (9th Cir.2004) ("service in the armed forces of the United States, along with the taking of the standard military oath, does not alter an alien's status to that of a 'national' within the meaning of the Immigration and Nationality Act").

CITIZENSHIP
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.

Eleventh Circuit

NATURALIZATION - NATIONAL OF THE UNITED STATES
Tovar-Alvarez v. U.S.Attorney General, ___ F.3d ___, 2005 WL 2561503 (11th Cir. Oct. 13, 2005) ("Though 8 U.S.C. 1101(a)(22) states that a person is a "national of the United States" if he owes "permanent allegiance to the United States," the manner in which one comes to owe allegiance to the United States is through birth or naturalization pursuant to the statutory scheme enacted by Congress, see 8 U.S.C. 1401-1409, 1421-1458. Sebastian-Soler, 409 F.3d at 1286. Moreover in Sebastian-Soler, we specifically rejected the Fourth Circuit's reasoning in Morin. 409 F.3d at 1287. Because Tovar-Alvarez was not born in the United States and has not been naturalized, he is not a United States national.").

NATURALIZATION COMPLIANCE WITH FORMAL CEREMONY REQUIRED BEFORE CITIZENSHIP IS CONFERRED
Tovar-Alvarez v. U.S.Attorney General, ___ F.3d ___, 2005 WL 2561503 (11th Cir. Oct. 13, 2005) (noncitizen must participate in public citizenship ceremony in order to fully naturalize).

IMMIGRATION STATUS - NATIONAL OF THE UNITED STATES
Sebastian-Soler v. U.S. Attorney General, ___ F.3d ___, 2005 WL 1174069 (11th Cir. May 19, 2005) (taking of oath of allegiance before Immigration Officer does not satisfy exception under which oath can be taken before a judge in alternate location; asserted permanent allegiance to United States was insufficient to make him national of United States).

Other

ILLEGAL REMOVAL OF UNITED STATES CITIZENS
Occasionally, persons are placed in removal proceedings, and even removed, even though they are United States citizens. E.g., Diaz v. Reno, 40 F.Supp. 2d 984 (N.D. Ill.1999) (U.S. citizen who had been ordered summarily excluded from the United States mounts several claims related to summary exclusion after returning to the United States); Fierro v. INS, 66 F. Supp. 2d 229 (D. Mass. 1999) (court enjoins removal of individual pend-ing resolution of claim to United States citizenship).

CITIZENSHIP - FOUNDLINGS
INA 301(f) allows "a person of unknown parentage found in the United States while under the age of five years" to be considered a citizen of the United States unless the person is "shown, prior to his attaining the age of twenty-one years, not to have been born in the United States."

UNITED STATES NATIONAL
New form I-9 has a box for US Nationals, apart from box for US citizens.

CITIZENSHIP - PROOF OF - CENSUS INFORMATION
United States Citizenship may be sometimes proven by showing a child appeared on a U.S. census in the United States shortly after birth. Contact US Census Bureau. Thanks to Mary Lee Eldridge