In November 2020, the Supreme Court will hear oral arguments in California v. Texas, where the plaintiff argues that the entire ACA is unconstitutional in the absence of the individual mandate penalties. Researchers in the Urban Institute’s Health Policy Center have spent much of the past decade compiling evidence on how the ACA has affected individual and family health care coverage, access, and affordability, as well as its implications for hospital finances and national health expenditures. We review this evidence and conclude that if the ACA is overturned, the consequences will be devastating for millions of Americans. Nearly 20 million Americans would lose health insurance coverage, and these coverage losses would cross numerous demographic and socioeconomic groups. Access to care and family financial security could also decline, and states and providers would face financial distress as federal spending and reimbursement shrink dramatically. The negative health and financial implications for individuals, families, and health care providers would be especially pronounced for many of the same populations faring worst under the pandemic and associated economic crisis.