Seventh District Republican Rep. Eric Cantor has helped lead the fight against Obamacare. But the Republican majority leader’s continued tenure in the House of Representatives may be the key to allowing Democratic Gov. Terry McAuliffe to win the Medicaid expansion envisioned by the very law Cantor opposes.  While counterintuitive, let’s examine this political logic.

In a last-gasp effort to avoid going the way of the Know-Nothings of the 1850s, Virginia Tea Party luminaries have united in an effort to defeat Mr. Cantor in his upcoming primary. We have previously written on his challenger’s generally lackluster campaign. But underdog Dave Brat’s backers say their low-key strategy is purposeful, centered on this mathematical calculation: A depressed turnout increases the importance of the Tea Party’s small but passionate voting constituency.

We are skeptical. But primary elections amid rampant anti-Washington feelings worry establishment figures such as Mr. Cantor. He is rumored to be preparing a full-scale campaign to avoid any surprises arising from complacency. The first signs of that effort appeared Wednesday, as Cantor rolled out his first television ad.

Watching the Cantor-Brat contest closely are Republican lawmakers in the House of Delegates. The great majority of them share Cantor’s situation: They are overwhelming favorites to win the 2015 general election in a gerrymandered Republican district. Their vulnerability, though, is in a low-vote nomination process with a challenger running as the “true Republican” against a RINO — “Republican in Name Only” — incumbent.

Cantor’s former statehouse colleagues view him as the canary in the coal mine. What if the House majority leader and heir apparent to Republican Speaker John Boehner fails to win easily?

The answer: They will likely eat ground glass before voting for anything a primary opponent could label as Obamacare. This already helps explain their current “Hell, no” to McAuliffe’s push to expand Medicaid, since many Republicans see it as little more than an extension of Obamacare.

The Cantor-Brat primary isn’t until early June. This is nervously close to the June 30 date when the current state budget expires. Unless the General Assembly agrees on new spending authority, Virginia faces a possible government shutdown on July 1. This has never happened before in Virginia.

We believe both parties are engaged in game of chicken, even as each side claims to be standing on principle.

How does this game end? The GOP’s “Hell, no” to Medicaid expansion actually gets its first internal voting test this month. Anti-expansion stalwart Del. Bob Marshall is the main, though under-funded, challenger to fellow Del. Barbara Comstock for the Republican nomination  in the 10th Congressional district. His side is painting Comstock as insufficiently anti-expansion, another RINO. But the 10th District Republican nomination is being settled in a canvass-type firehouse primary, which is guaranteed to produce a far lower turnout than a normal primary. It is unclear what conclusions other GOP delegates around the state will draw from those results.

In Cantor’s case, however, the fight is being conducted according to the usual rules, including the option for Democrats to vote. But Tea Party fear still haunts Republicans who reversed course last year to back a record transportation tax increase. That, coupled with the possibility of being labelled pro-Obamacare in a GOP primary, creates a political emergency not curable by the even the most free market of Medicaid plans.

Cantor helped lead the GOP fight on Capitol Hill against Obamacare. But if Republican delegates start believing even those repeated efforts to repeal the health insurance law weren’t enough to ensure an easy win against Brat, then our prediction of no government shutdown will be severely tested.

Norman Leahy is an editor of the conservative Web site and producer of the political radio show “The Score.” Paul Goldman is a former chairman of the Democratic Party of Virginia. They are blogging together on All Opinions Are Local during Virginia’s 2014 General Assembly session.