Does your boyfriend have a birth certificate stating that his father was American? Was the birth certificate issued by the American Dept. of State? I am not a lawyer but you might want to do an internet search.
If the one parent of your fiancé was an American Citizen than he may have a good chance to come into the country.
WAC is the Washington State Administrative Code which is written by the Legislature of the State of Washington. It is similar to a parliament. The Congress has the authority to write immigration law under the Federal Constitution not each state in the union but the state of Washington is following Federal law.
The USA is a federal constitutional republic and not a democracy. Many Americans are confused about this also.
WAC 388-424-0001 Citizenship and alien status - Definitions
You might want to go to the following web page.
U.S. citizens" are one of the following:
a. Individuals born in the United States or its territories (Guam, Puerto Rico, and the U.S. Virgin Islands; also residents of the Northern Mariana Islands who elected to become U.S. citizens).
b. American Indians born outside the U.S. without regard to immigration status or date of entry if:
i. They were born in Canada and are fifty percent American Indian blood (but need not belong to a federally recognized tribe); or
ii. They are members of a federally recognized Indian tribe or Alaskan Native village or corporation.
c. Individuals who have become naturalized U.S. citizens.
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**d. Individuals born abroad to at least one U.S. citizen parent depending on conditions at the time of their birth, per title 8, subchapter III, section 1401 of the United States Code.
e. Individuals who turn eighteen years of age on or after February 27, 2001, automatically become U.S. citizens if the following conditions are met while the individual is under age eighteen per INA 320.
i. The individual is granted lawful permanent resident (LPR) status;
ii. At least one of the individual's parents is a U.S. citizen by birth or naturalization; and
iii. The individual:
A. Resides in the U.S. in the legal and physical custody of the citizen parent; or
B. Was adopted according to the requirements of INA 101 and resides in the U.S. in the legal and physical custody of the citizen parent.
f. Individuals who turned eighteen before February 27, 2001, would have automatically become a citizen if, while the individual was still under eighteen, he or she became a lawful permanent resident and both his or her parents naturalized. Such individuals also may have derived citizenship when only one parent naturalized, if the other parent was dead or a U.S. citizen by birth, or the individual's parents were separated and the naturalized parent had custody.