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. 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).Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. The person does not have a legal guardian or the state or a designee of the state is the legal​. 3.7 guardian of the person;​.