Nearly every Republican governor refused to set up an exchange, under pressure from conservatives who described it as an embrace of Obamacare. A ruling against the subsidies could put health coverage out of reach for hundreds of thousands of middle-income constituents and risk sending their insurance markets into a "death spiral" as costs rise and healthier customers drop out.
Here are the top five Republican presidential hopefuls who would be harmed.
Scott Walker of Wisconsin
The Wisconsin governor, who has been surging in the 2016 Republican polls, would face political dangers on several fronts. About 170,000 Wisconsinites would lose their subsidies, according to a recent study by Harvard's Theda Skocpol and the University of Minnesota's Lawrence R. Jacobs. That's a massive headache to withstand. But there's more.
As Josh Green reports for Bloomberg Politics, Walker has used Obamacare as an off-ramp to cut his state's spending on health care. He has funneled an estimated 83,000 low-income people from the state's Medicaid program, called BadgerCare, onto the federal government's dime under Obamacare. These people could also lose their coverage if Obamacare goes down in Court.
Wisconsin's legislature is controlled by Republicans, who would be under pressure to reject a state exchange even if Walker wanted to set one up.
Chris Christie of New Jersey
Roughly 200,000 New Jerseyans enrolled on the federal exchange could lose their coverage. The Democrats who run the state legislature may push for setting up a state-run exchange to mitigate the damage, forcing Christie into an unenviable dilemma. He would have to choose between leaving a huge number of constituents out in the cold and angering core Republican voters by embracing a core component of Obamacare.
John Kasich of Ohio
An estimated 185,000 Ohioans would lose tax subsidies under Kasich, who won a blowout reelection victory in 2014 and has roused 2016 speculation with upcoming trips to early primary states New Hampshire and South Carolina.
Kasich faces a unique problem because, unlike many Republican colleagues, he adopted Obamacare's Medicaid expansion for Ohio. A loss for the ACA in the Supreme Court means the Ohio's low-income residents under 133 percent of the federal poverty level would be eligible for government-subsidized care through Medicaid, but middle-income residents between 133 percent and 400 percent of the poverty level would suddenly become ineligible.
What can Kasich do? He faces a Republican legislature that would be under enormous pressure to resist building a state exchange. But he has a bigger problem: Ohio voters passed a constitutional amendment in 2011 to effectively disapprove of Obamacare that arguably prohibits it from building an exchange.
Susana Martinez of New Mexico
The first female governor of New Mexico and the nation's first Hispanic female governor has been floated as a 2016 contender, albeit more so as a vice presidential prospect. Under her watch, more than 50,000 have signed up for an Obamacare plan, and a vast majority could lose their coverage if the subsidies are struck. It will depend on the specifics of the Supreme Court's ruling — New Mexico is one of few states with a federal-state partnership exchange; it has been using HealthCare.gov for enrollments.
If the state's subsidies are struck, Martinez faces a similar landscape as Kasich: New Mexico adopted the Medicaid expansion, so its low-income residents would enjoy subsidized coverage but middle-income residents would lose it.
Bobby Jindal of Louisiana
Upwards of 180,000 Louisianans have signed up for an Obamacare plan under Jindal's watch. Losing their subsidies would be unhelpful for Jindal's record and (already slim) presidential prospects, as his state already ranks in the top 5 when it comes to highest uninsured rates.