The stakes of the Supreme Court’s looming decision on Obamacare have just been raised.   Last week, the Commonwealth Fund released results from a Health Insurance Tracking Survey of Young Adults, which estimates that 13.7 million young Americans ages 19 to 25 joined or remained on a parent’s health insurance plan between November 2010 and November 2011. Of those, 6.6 million—myself included—would not have been able to do so without the Affordable Care Act.

That figure is a significant jump up from the Obama administration’s previous estimate, which put the number of young adults newly insured thanks to the ACA at 2.5 million. The provision extending coverage for dependents until their twenty-sixth birthday was one of the first pieces of the ACA to make a significant dent in the ranks of the uninsured, and it has been one of the most popular parts of the controversial law. More than 70 percent of Americans view the provision favorably. Its effects have been felt all the more strongly in an economic climate that is particularly hostile to young adults; in May, unemployment for 16-to-24-year olds was nearly double the national average.

The popularity of that piece of Obamacare has not been lost on politicians. Some Republican lawmakers appear to be rethinking their condemnation of the entire law on principle. In early May, Massachusetts senator Scott Brown, who has voted to repeal the ACA on three occasions, acknowledged that he was taking advantage of the law to insure his 23-year-old daughter. Then, Missouri senator Roy Blunt broke ranks with his party, saying in an interview that the “dependent coverage” provision “should continue to be the case.” Georgia representative Phil Gingrey, who co-chairs a caucus of twenty-one Republican lawmakers with medical backgrounds, called the young-adult provision “good policy,” and also expressed support for insuring those with pre-existing conditions. It isn’t clear how Republican lawmakers plan to pay for the popular parts of the law they say they would like to keep, particularly regarding pre-existing conditions. Mitt Romney, for his part, has pledged to steamroller the law in full.

The new findings underscore the significance of the Supreme Court’s ruling, which will come before the month is up. The popular pieces of the law are in jeopardy even if the court strikes down only the individual mandate, since the mandate is what makes the rest of the law financially feasible. Extending coverage for dependents is one of the easier provisions to finance, but it seems unlikely that lawmakers could overcome the partisan impasse in order to refashion any sort of health reform if the ACA is dismantled. Last month, Health and Human Services Secretary Kathleen Sebelius and Education Secretary Arne Duncan sent a letter to college administrators and student groups regarding the implications of the dependent coverage provision. “Before the new health care law…graduation day was the day when millions of young adults lost their health insurance,” they wrote. “Now, graduating students are free to make career choices based on what they want to do, not where they can get health insurance.”

For more on Obamacare and young adults, see my article “Will Millions of Young Americans Benefiting From the ACA Turn Out for Obama?”