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).Proof of US citizenship or permanent resident status. Federal tax return or IRS tax transcript for the most recent year. Typically, in order to claim US domicile, the Affidavit of Support sponsor must be residing in the United States. The official website of the U.S. Air Force.