It’s been two months since the last major push to repeal the Affordable Care Act died in the Senate, but the law is still on the ropes. Republican efforts to stymie the law and dismantle connected pieces of the national health infrastructure are taking their toll. With or without a full repeal, policy developments on the horizon could topple Obamacare, causing millions to lose coverage or see their health-care costs increase beyond their ability to pay. Very few pieces of the health law aren’t vulnerable right now. To start, it turns out that despite numerous reports of “surges” in sign-ups on, the federal-exchange website, at the beginning of the open-enrollment period in November, overall uptake might still be anemic compared with last year. This was the desired result on the part of the White House. The Trump administration slashed the open-enrollment advertising budget and halved the sign-up period this year. That means that in order to outpace 2016’s numbers on the federal exchange, enrollment would have had to start strong and outpace every 2016 benchmark. Buoyed by promotion from health-care companies and private citizens—including Barack Obama—a strong start materialized, but the pace has recently slipped. So far, 2.3 million people have signed up for coverage on the federal exchange, but about 7 million more would need to enroll before the end of open enrollment on December 15 to match last year’s numbers. If this year’s enrollment falls short, it could further imperil exchanges that are already at risk. Insurance companies plan both their rates and their participation in the exchanges based on future margins, which depend on both the volume and health of enrollees. Existing instability on the exchanges—and GOP “sabotage”—have already increased premiums, although most consumers don’t actually see those rising costs because federal subsidies hide them. But with the addition of more uncertainty, generated by the administration’s refusal to make cost-sharing-reduction payments to insurers, there’s a greater incentive to leave markets altogether or find ways to select against poorer enrollees. The number of counties with no insurers offering