The other day, Republican businessman Vance McAllister defeated a fellow GOPer in a Louisiana House special election, even though he supports the Medicaid expansion, which is of course a feature of the hated Obamacare. While there’s some argument as to how much the expansion meant to the outcome, McAllister’s willingness to embrace the idea of accommodating a part of the health law to bring in federal money suggests something of a schism between pragmatic and ideological Republicans over the issue.

Now the Daily Caller’s Matt Lewis reports that opposition to the Medicaid expansion is set to become a major litmus test issue in GOP primaries:

The issue is now making its way into Idaho’s Second Congressional District —  in what is shaping up to be a brutal primary between Rep. Mike Simpson and  a conservative challenger named Bryan Smith.

In a press release earlier today, The Club for Growth, a powerful fiscally  conservative group,  pointed out that a Super Pac backing Simpson has also endorsed expansion. (It’s not clear where  Simpson stands on the issue, and that’s sort of the point.)

“Does Mike Simpson support or oppose expanding Medicaid under ObamaCare in  Idaho, just as his supporters in the Idaho Association of Commerce and Industry

do?”   asked Club for Growth Spokesman Barney Keller in the release. “Medicaid  expansion will cost taxpayers billions and stick future generations with the  bill. Conservatives across the country are rejecting ObamaCare’s Medicaid  expansion, and Mike Simpson should have to answer if he joins with the Idaho  Association of Commerce and Industry in supporting ObamaCare’s Medicaid  expansion in Idaho.”

If Idaho is a harbinger of things to come, expect Medicaid expansion to be a  huge issue in Republican primaries — a sort of litmus test for true conservatives.

Meanwhile, House conservatives are beginning to hatch a new strategy for the coming budget talks that would involve pushing for a defunding of the law’s Medicaid expansion, and using the money to offset the sequester’s defense cuts. Though this idea seems to have very little support, it’s not impossible it could gain some momentum.

And in Tennessee, the Republican governor is coming under increasing pressure from local business interests who want him to embrace the Medicaid expansion. He is caught between GOP lawmakers who oppose the expansion, and hospital groups and the local chamber of commerce, who want it.

At the same time, the Medicaid expansion seems to be emerging as a bit of a political bright spot for Dems.

In Louisiana, where Senator Mary Landrieu is supposed to be running away from Obamacare, Dems are actually seizing on the McAllister victory as proof that the Medicaid expansion is good politics among middle of the road voters. Dems are attacking her GOP challenger, Rep. Bill Cassidy, for opposing the expansion in the state. And Terry McAulliffe just won the governor’s race in Virginia — which Republicans widely cast as a “referendum on Obamacare” — while frequently citing the Medicaid expansion. It has solid majority support in states such as Pennsylvania and Ohio, which might explain why Republican governors in those states have embraced the idea.

Democrats increasingly believe that, at a time when the law known as “Obamacare” is suffering serious rollout travails and is sinking in polls, the Medicaid expansion is a good issue for them — one that neatly shows that some of the individual provisions of the law remain politically viable, and as an added bonus could even divide Republicans. Obamacare’s expansion of coverage is most pronounced in the Medicaid expansion area, which could make it politically more difficult over time for Republicans to oppose it — even as conservatives appear poised to continue making opposition to it a defining issue. Whether this emerges as a real wedge among Republicans will be something to keep watching.