A spurt of Republican states changing their minds on Medicaid expansion backs up an optimistic argument you hear a lot in health-policy circles: It took a long time for all 50 states to sign up for the original Medicaid program, and the expansion will unfold in the same way — slowly but surely.

If the analogy holds, the takeaway is not to get too concerned about Medicaid expansion: Even the reddest states can only deny federal money to their hospitals, doctors and insurers for so long, which means that poorer Americans in every state will get coverage eventually. The federal government should keep doing what it's doing – offering compromises, and letting pressure from state lobbying groups do the rest.

But interviews with hospital and insurer associations in states that have yet to expand Medicaid suggest that "eventually" could be a lot longer this time around. If so, the federal government might need a change in tack, as it tries to extend coverage to almost 5 million people.