“Notice the word “If”. United States law does not recognize that American citizenship may be lost as the result of adoption.”
That is true, at least not permanently. Once you attain 18 years of age, the law affords that former citizen the right to go before the appropriate State Dept. official and swear an oath of allegiance to the US. At that time you become newly naturalized, and forever lose natural born status.
We would also like to see evidence of Hussein ever having made such an oath of allegiance.
United States law does not recognize that American citizenship may be lost as the result of adoption. There is nothing to regain, the minor always remains an American citizen, there is no reason to go through naturalization.