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). A declaration is a simple statement that you intend in good faith to return to the United States to resume your domicile.Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. Explore I-864 Affidavit of Support: Financial duties, divorce implications, income calculation. Get guidance from skilled Los Angeles immigration attorneys. These additional financial sponsors also have to submit an Affidavit of Support, proof of their income, and proof of their legal status in the United States. Get a certified copy of your birth certificate.