Earlier today, the only remaining Obamacare insurer in most of Iowa announced it would probably stop selling plans there next year. This afternoon, there's more trouble for the healthcare law in the Old Dominion, where Aetna will no longer sell plans beginning next year.

This means that at least 24 Virginia counties are likely to have only one choice of insurer on the exchanges next year, joining the roughly one-third of U.S. counties where Obamacare has already resulted in a local monopoly in the subsidized health insurance market as of this year.

Virginia may not be the last state where Aetna pulls the plug, either. It already did so in Iowa (before the smaller company Medica did so today), and it's still pondering its future in Nebraska and Delaware, the other two states where it still sells individual plans. Until this year, the company had sold plans in 15 states.

Aetna claims it lost $680 million before taxes on individual Obamacare insurance plans in the law's first three years of operation, with the losses growing each year, and it expects to lose money again in 2017.

Democrats can say what they like about Republicans doing various things to make Obamacare fail. But quite a few insurers quit many states before now. How many big players in the industry with experience selling insurance have to decide they can't make money under this law, despite the subsidies, before everyone has to admit there's a structural problem with the law itself?