Texas Gov. Rick Perry announced Monday morning his intention to opt out of the Affordable Care Act's Medicaid expansion. That adds Texas to the five dark-red states, mapped out below, that have already made simple promises:

Six governors may not seem like a lot, but consider this: A full quarter of the 15.8 million Americans expected to gain Medicaid under the Affordable Care Act live in these states. These six governors, if they follow through on their pledges, can single-handedly shrink the Medicaid expansion by 3.89 million people.

Some of those people would find coverage on the health insurance exchange: Those who live above the poverty line would be eligible for subsidized coverage. Most of those eligible for the Medicaid expansion, however, aren't in that situation. Three-quarters live below the federal poverty line. The law assumed these individuals would end up on Medicaid, and did not include any provisions to provide private insurance.

It's hard to know what, exactly, states will do come 2014. We don't know whether they will stick to their promises and, if they do, how long states will resist the lure of federal funding. We do, however, know that much of the health law's future now rides on what decision these governors ultimately make.