Prior to any decision on the fate of the mandate, the Congressional Budget Office estimated that the Affordable Care Act would cover more than 30 million Americans by 2022:

Data: CBO, Graph: Ezra Klein

Health care economists roundly agree that number would decrease without a requirement to purchase health insurance. They disagree, however, about how much:

Source: America's Health Insurance Plans

They also agree that the cost of health insurance would increase although, again, they disagree about whether that would be a slight increase in cost or a huge spike:

If premiums go up, so does the cost to taxpayers of insuring each individual. That's why overturning the mandate might not mean the law spends less money: Even though we're insuring fewer people, each one is costing us much more. Moreover, the people we're insuring are, on average, quite a bit sicker, as healthier folks are hanging back from the market. The Economic Policy Institute estimates that "the cost per newly insured person under health reform without the mandate is 93.3 percent higher than under health reform with the mandate."

Throughout the health care debate, the individual mandate has proved the health reform law's least popular provision. The last time the Kaiser Family Foundation polled on the issue, it found just 30 percent of Americans had a favorable opinion of the health reform provision:

What no one knows, at least right now, is how public opinion -- and, importantly, congressional opinion -- changes toward the bill if the mandate is excised.