One of the core purposes of the Affordable Care Act is to expand health care to people who previously lacked it, and today Gallup-Healthways released new numbers showing once again that the law is accomplishing this goal.

But buried in the data is an indicator of a different kind of success: Republican resistance to the law at the level of states is also having a substantial impact by limiting the drop in percentages of uninsured people, keeping the uninsured rate higher than it might otherwise have been.

Here’s how: Gallup tells me that the numbers show that the drop in uninsured due in particular to the Medicaid expansion has slowed significantly since last year — because far fewer new states have expanded Medicaid in recent months compared to the block of states that did so initially at the start of 2014.

First, Gallup’s topline findings, which show a clear decline in the uninsured rate since the law took effect:

The uninsured rate among U.S. adults declined to 11.9% for the first quarter of 2015 — down one percentage point from the previous quarter and 5.2 points since the end of 2013, just before the Affordable Care Act went into effect. The uninsured rate is the lowest since Gallup and Healthways began tracking it in 2008.

While Gallup concludes that the improving economy may be playing a role, it also notes that the uninsured has now dropped significantly lower than it was in early 2008, before the worst of the economic crisis, suggesting that the law is a key factor. And Gallup adds that the drop in the uninsured rate is particularly pronounced among lower income Americans (down 8.7 percentage points since the law went into effect), African Americans (down 7.3 points) and Latinos (down 8.3 points).

That’s great. But Dan Witters, the research director of the Gallup-Healthways Well-Being Index, tells me the numbers also clearly show a drop-off in the impact of the Medicaid expansion on the uninsured rate — a drop-off that coincides with the slowdown in GOP states opting into the expansion.

Witters says that Gallup data — which are extremely extensive, a key reason why this polling is the gold standard for measuring the law — showed that last year’s drop in the uninsured rate, which was 4.6 percentage points, was heavily fueled by the Medicaid expansion. The expansion was responsible for around 40 percent of the newly insured, he says.

But this year, the drop has thus far been only 1.5 points — in part because of the Medicaid expansion slowdown. The data show that the fall in the rate in uninsured this year due to the Medicaid expansion is only about three-tenths of a percentage point, he says.

“The states that are expanding Medicaid in recent months have only been trickling in — there are fewer new states expanding Medicaid in 2015 as opposed to 2014,” Witters says. “That has sucked the air out of the rate of decline this time, relative to the last. The rate of decline in the uninsured has dropped across all American adults, in part because fewer states are joining in the Medicaid expansion.”

After a number of states expanded Medicaid last year, in 2015 the push for the expansion has stalled in places like Florida, Tennessee, Alaska, Missouri, and Utah, due to conservative legislative opposition and an aggressive campaign against it by the Koch-founded Americans for Prosperity.

Witters says the data suggests that if the expansion had proceeded at a comparable clip this year, the uninsured rate would have shown an even “more accelerated decline this time, a decline pretty close to what we saw the first time around.” He adds: “We’d probably see around another point shaved off — and every percentage point is another 2.4 million American adults.”

Florida might end up opting in to the Medicaid expansion. GOP governor Rick Scott’s sudden reversal on the expansion has put the state’s budget negotiations — including planned tax cuts, a major GOP priority — in peril, and some GOP legislators are insisting on the expansion to move the budget process forward, which suggests its fiscal logic may ultimately carry the day. That logic may yet prevail in other states where the expansion is being debated.

But it’s very possible the Medicaid expansions could remain on hold. And beyond that, of course, looms the Supreme Court’s pending decision in the King v. Burwell lawsuit, which could gut subsidies for millions in the three dozen states where governors have declined to set up exchanges, possibly driving the uninsured rate back up again. Which is to say that even if the law currently is accomplishing one of its core goals, GOP resistance to it is accomplishing one of its core goals, too — and the resistance’s achievements could only grow more impressive in the months ahead.