Chris Christie New Jersey Gov. Chris Christie (Mel Evans / AP)

Chris Christie today joined seven other Republican governors — so far — by choosing to opt in to the Affordable Care Act’s Medicaid expansion. As Christie tweeted, “Accepting these federal resources will provide health insurance to thousands of low-income New Jerseyans and actually save taxpayers money.”

Remember, making Medicaid expansion optional was the big GOP win from the Supreme Court decision that otherwise disappointed conservatives by leaving the ACA in place. But Christie joins Republican governors in Florida, Ohio and other states in finding the federal money (and, perhaps, the increased coverage) impossible to resist.

The future of this is now pretty clear: It’s going to work just as the original Medicaid roll-out did. That was also optional for states, and many of them declined the first time around, but eventually all 50, no matter how conservative, found themselves participating. The key — and I expect this to be true of the ACA Medicaid expansion as well — is that the decisions were one-way. Over time, some of the decliners decided to join, but no state walked away.

In practical terms, this means that a lot more Americans are going to have health coverage: 3.2 million in just those eight states alone.

The remaining question is: Will Republican governors pay any price in national politics for accepting Medicaid expansion? For any governor who has national ambitions, the hope has to be that the expansion rapidly shifts from a betrayal of Republican principles to something that almost all the states are doing. Otherwise, it’s almost certainly going to be a weapon used against them.