If you want to sponsor someone for a family-based green card, you need to provide proof of a U.S. domicile in your Affidavit of Support (Form I-864). On Form I864, petitioners must prove that they have the ability to financially support the visa applicant(s) if necessary.This guide will explain how to prove domicile when filling out Form I-864 ("Affidavit of Support"). Consular processing support without the high price tag. Completing and signing Form I-864 makes you the sponsor. This guide will clarify what domicile is, how to establish it, and the documentation you need for proof of domicile. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States.