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).Completing and signing Form I-864 makes you the sponsor. If you have a joint sponsor, the joint sponsor must also complete and sign USCIS Form I-864. Learn the what, why, and how of filing a form I-864 affidavit of support for US immigration. In this video we're going to show you how to complete an i 864 and affidavit of support that is needed as part of the package for an adjustment of status. Driver's License or State ID: As it shows your permanent residence, a valid U.S. driver's license can act as proof of domicile.