The Form I-864 Affidavit of Support is a legally enforceable contract between you and the U.S. Government with the intending immigrant as a third-party beneficiary.
That means that when a sponsor signs Form I-864, and the intending immigrant becomes a lawful permanent resident of the U.S., either the government or the sponsored immigrant can take the sponsor to court to enforce the Affidavit of Support.
When the government sues the sponsor, it can ask to be reimbursed for the amount of means-tested public benefits that have been provided to the immigrant.
When the immigrant sues, he or she can collect enough money to bring his or her income up to 125% of the amount listed in the U.S. government’s Poverty Guidelines (as shown in the chart in Form I-864P).
You might think, can’t I do a pre-nup to protect myself? The law is unclear on whether a pre-nuptial agreement can protect a sponsor from the immigrant suing the sponsor for support.  Although in no way guaranteed, the best chances of avoiding an immigrant suing the sponsor for support is to have the immigrant/Permanent Resident execute a “Waiver” of their right to support pursuant to the Affidavit of Support as part of a divorce settlement. 
The execution of a waiver that specifically refers to a relinquishment of right to support pursuant to the I-864 Affidavit of Support (not just spousal support or maintenance in accordance to state law) is important because the sponsor’s responsibility does not end with divorce itself but rather lasts until the immigrant becomes a U.S. citizen, has earned 40 work quarters credited toward Social Security (a work quarter is about three months, so this means about ten years of work), dies (or until sponsor dies), or permanently leaves the United States.
Even a bankruptcy does not necessarily end your I-864 obligations. Although most debts and contractual obligations are dischargeable in bankruptcy, so-called “domestic support obligations” are one exception. Such obligations are defined as alimony, maintenance, or support owed to or recoverable by one’s spouse, former spouse, or child. Under U.S. court decisions—for now—these also include I-864 support obligations.
Your rights and responsibilities are specifically explained in the form itself, but don’t take the signing of an I-864 lightly! If you or your spouse secured immigration status in the United States through marriage, make sure your divorce attorney understands the importance of addressing the continuation or termination of the contractual support obligation pursuant to the Affidavit of Support during the divorce process. Sterling Law Office does! www.sterlinglawoffice.net / 231-486-0559
 Toure-Davis v. Davis, Civil NO. WGC-13-916, 2014 U.S. Dist. LEXIS 42522 (D.Md., March 28, 2014); Blain v. Herrell, No. 10-72 ACK-KSC, 2010 U.S. Dist. LEXIS 76257, 2010 WL 2900432 (D. Haw. July 21, 2010); Erler v. Erler, CV-12-02793-CRB, 2013 WL 6139721 (N.D. Cal. Nov. 21, 2013).
 Affidavits of Support on Behalf of Immigrants, 71 Fed. Reg. 35732, 35740(June 21, 2006) (but clarifying that a sponsor’s duties to reimburse government agencies would remain unchanged).