The GOP’s relentless assault on Obamacare hasn’t succeeded in repealing or defunding the law, but it has managed to do something: prevent a lot of uninsured Americans from getting health insurance.

With three months of Obamacare enrollment completed, the effect of the Republican intransigence on health care reform can be seen in new data compiled by Theda Skocpol, professor of government and sociology at Harvard University and director of the Scholars Strategy Network.

Though it is a federal law, the Affordable Care Act is a program that relies on states. States had the opportunity to set up its own health insurance marketplace, and states were heavily incentivized to expand Medicaid to cover their poor — though the choice was up to them.

Largely as a result of the entrenched opposition of state GOP leaders, only 14 states (plus D.C.) have built their own marketplaces, and just half the states decided to expand Medicaid in the first year. Heading into 2014, those two state-based decisions have created a huge disparity between states under the law.

Skocpol has quantified that disparity in the chart above — see the larger version. She’s attempted to measure how much progress different groups of states — those that both expanded Medicaid and built their marketplace, for example — have made in signing their residents up for private coverage and Medicaid under Obamacare.

The difference between the top and the bottom groups tells the whole story. Those states, like California and New York, that have fully bought into the ACA have performed exceedingly well in enrolling their citizens. They’re already 43 percent of their way toward their projected Medicaid enrollment, as calculated by Skocpol, and 37 percent of the way there on private coverage.

But as involvement goes down, so does enrollment. Those states, like Florida and Texas, that decided to opt out completely have only enrolled 1.5 percent of their potential Medicaid population if they had expanded the program as originally planned. By leaving their citizens to deal with problem-plagued HealthCare.gov, private enrollment is struggling, too: Only 5.6 percent toward the mark.

That means that thousands in those “Just Say No” states are going without coverage because their state leaders stubbornly refused to participate in any way, shape or form in Obamacare.

“You go back to how the law was designed, for better or worse, it gave states a lot of responsibility,” Skocpol told TPM. “The states that have actually done things the way the law envisaged are the ones that are, at this early stage, doing the most toward those goals.”

“But the ‘Just Say No’ states are putting all their lower income residents at risk,” she continued, “not just by refusing to expand Medicaid but also, in many cases, by failing to help people get subsidized private coverage through the exchange.”

A few things to keep in mind. First, these are aggregate numbers. Some “Full-Go” states like California and Kentucky have had excellent Obamacare experiences so far, but others, like Hawaii and Oregon, have struggled mightily. Second, the “Just Say No” states have had their private coverage enrollment slowed thus far by the failures of the federal government’s HealthCare.gov website.

Lastly, it’s likely that the numbers, at least for private enrollment, will narrow before the end of open enrollment in March. The data that Skocpol used included more recent enrollment figures for state marketplaces, but nothing more recent than Nov. 30 for the states using HealthCare.gov. The Obama administration has said that about 975,000 enrolled nationwide through the federal site in December.

But the underlying narrative will likely persist, especially if states continue to refuse the Medicaid expansion. Those that bought into the law will go a long way toward covering their uninsured; those that haven’t will continue to leave a major portion of their uninsured without coverage.