Can I fix my Mexican fiancé's citizenship?

A U.S. citizen may apply for a fiance? to enter the U.S. for the purpose of becoming married within the required time, and then following the wedding the couple jointly may complete the process for adjustment of status to become a Lawful Permanent Resident (to get a "Green Card"). Approximately three years after getting a "Green Card," the foreign national spouse may apply to become a naturalized U.S. citizen. The application process can be significantly more complex than it may first appear, and improper preparation or inadequate documentation may cause significant delay or even more harsh consequences. It would be wise for you and your fiance to consult with an immigration attorney, who, after learning all of the relevant information about your fiance, could advise about eligibilities, options and strategies, including likelihood of success, total costs, etc.