If you want to know which news item will be making Gibbs look constipated at tomorrow’s briefing, look no further. It’s the first time voters from any state have addressed the mandate at the polls.

And things are looking good.

Opponents of Prop C — those who support the insurance mandate — have been frustrated by the lack of a vigorous campaign to defeat it. Apart from a mass mailing by the Missouri Hospital Association, no organized effort existed until a few weeks ago when three 19-year-olds started a Facebook campaign. “I’ve had to spend about $500 out of my own pocket making signs,” lamented Caleb-Michael Files, the Subway sandwich-shop manager and full-time college student who launched the Facebook effort. He wonders why Missouri is spending money on a referendum likely to stir up an expensive court case. “The law is the law,” he says. Missouri lieutenant governor Peter Kinder is one of several state officials across the country who have already filed suit challenging the federal law. (Another of those, Virginia attorney general Ken Cuccinelli, gained a small victory in his fight against the law on Monday, when a federal judge ruled that the state does indeed have standing to bring the suit.)

Prop C is a gimme for the GOP base. In polls, Republicans strongly oppose Obamacare — and Tuesday’s primaries are far more interesting on the GOP side, practically guaranteeing a turnout heavily skewed against health care reform. Republicans barely need to raise more money to get out the vote.

Democrats in the state legislature actually colluded to make sure it was on the ballot today so that they wouldn’t have to risk an even more embarrassing result in November. Here’s the actual text of the proposition together with real-time polling results. It’s symbolic, of course: Strictly speaking, it would deny the government of Missouri the power to penalize citizens for failing to buy health insurance, but that’ll be irrelevant if/when a federal court decides that the mandate in ObamaCare is constitutional. This is pure politics, aimed at reminding Democrats that even in a perennial swing state, opposition to compulsory insurance isn’t a close call. Too bad the vote didn’t happen a few weeks earlier, as a lopsided win might have scared a few centrist Dems away from other hot-button legislation like financial reform.

As I write this, with 282 precincts reporting, the anti-mandate vote leads … by 47 points. Scroll all the way down to the bottom here and follow along.

Update: With roughly a third of all precincts reporting, the anti-mandate vote is at … 75.8 percent. Good lord.