Democrats were ecstatic when a judge in Honolulu barred enforcement of the Trump administration's travel ban. They were thrilled when a judge in Chicago halted a policy to rescind grant funding to sanctuary cities. In both cases, the judges extended their ruling beyond the litigants to the whole country, issuing so-called national injunctions.

For opponents of Donald Trump's administration, this legal maneuver has seemed like a godsend. Now it may come back to haunt them, as a single federal judge in Texas considers putting the Affordable Care Act on ice—not only in Texas, but anywhere in the country.

Can one judge really impose his ruling from one coast to the other?

A group of Republican state attorneys general certainly think so. In their view, Congress knocked the constitutional legs out from under Obamacare when it repealed the penalty for going without insurance. They've sued to stop the federal government from implementing any part of the law—including its protections for preexisting conditions and the Medicaid expansion—across all 50 states.

What's more, they might win. Their legal arguments are thin, but the Republican attorneys general filed their case in Fort Worth, Texas, knowing they'd draw a conservative judge who'd be sympathetic to their cause. In a hearing, that judge suggested he was inclined to side with the attorneys general. Within weeks, he could issue an order enjoining all or part of the law.