The Affordable Care Act (ACA) required most Americans to enroll in a health insurance plan or pay a financial penalty — until Congress got rid of the penalty as part of last year’s tax law. But what would happen if every state followed the lead of Massachusetts and New Jersey by enacting its own individual mandate to replace the ACA’s version? According to a new Commonwealth Fund/Urban Institute report, close to 4 million Americans would gain health insurance and premiums would drop nearly 12 percent.