Washington insiders were stunned.

"Look," Gov. Chris Christie said to a packed house the other day. "We have to get real. We're going to double the number of people on Social Security and Medicare as the boomers retire. Even with aggressive cuts in the growth of these programs, taxes are going to have to rise. We've already got trillions in unfunded liabilities here. The math doesn't work without higher federal taxes.

"Oh, I said it," Christie added with an impish grin, "and I'm still standing. I did not vaporize into the carpeting!"

Maybe you heard about this. And about how all of Washington swooned. But of course I made this up. The "truth-teller" du jour (who unveiled a tough New Jersey budget Tuesday that sensibly asks public workers to pick up more of their health and pension costs) did not have the guts to speak this particular truth. Christie merely said that Social Security's retirement age would have to be raised and Medicare would need to be tweaked lest it bankrupt us - things that less sexy pols, such as Democrats Dick Durbin and Mark Warner, have noted without anyone fainting in admiration.

Now, don't get me wrong. I find Christie's brash style refreshing. But we're so accustomed to political flimflam that, as Daniel Patrick Moynihan might have put it, we're defining truth-telling down. For Christie to be rhapsodized for saying we need to reform entitlements without adding that federal taxes will have to rise as America ages makes him a half-truth-teller at best.

And half-truths are all we have from the GOP so far.

Thanks to House budget chief Paul Ryan, it's possible to measure the size of this fraud. And it's colossal. As can never be said often enough, Ryan is absurdly hailed as a fiscal "conservative" for a "roadmap" that doesn't balance the budget until the 2060s and that adds an unthinkable $62 trillion to the national debt between now and then. How can this be the case when Ryan puts forward trims for Social Security and Medicare so "bold" that most Republicans wouldn't dream of supporting them? Because Ryan also pretends we can keep federal taxes at their recent historic levels of 19 percent of gross domestic product as the boomers age.

No can do. The math doesn't work. Ryan's endless red ink proves this.

Christie's big straight-talk credential so far is his willingness to stare down the teachers unions. Their archaic practices need to be challenged, and Christie deserves credit for taking them on. But is it really "courageous"? Courage is when a politician tells his strongest supporters things they don't want to hear. I'm a little tired of Republicans calling for an "adult conversation" that mainly takes things away from adults who don't vote Republican.

No, until Christie steps up, the closest thing to a GOP truth-teller is Mitch Daniels, who may become a case study in how intellectually honest one can be in a GOP primary and still remain viable. For fiscal fetishists like me, ever alert for the truth-on-taxes dog whistle, Daniels hasn't disappointed. He's refused to take Grover Norquist's anti-tax pledge, telling Lawrence O'Donnell on MSNBC last month that "anybody running for president should pledge to take . . . only one oath, and that's the one that involves the Bible and the west front of the Capitol."

Then, in his thoughtful CPAC speech recently, Daniels said slaying the "red menace" of debt was of such paramount importance that conservatives needed to be open to "the second best way." "Purity in martyrdom is for suicide bombers," he said. "I for one have no interest in standing in the wreckage of our Republic saying . . . 'you should have done it my way.' "

We hear the whistle, Mitch! We hear you!

So, on the guts scorecard, we have Daniels signaling to conservatives that new taxes will be needed, and Christie telling the Democrats' biggest interest group that it's time to trim their pay and benefits. You be the judge.

Still, it's early days. I want Christie to rise to full truth-telling from half. I'm ready to make the pilgrimage to Trenton to walk him through the federal numbers, which are very different from his state's. The GOP fantasy that we can keep federal taxes at historic norms in an aging America is a major obstacle to sane governance. Given the devotion Christie inspires among the GOP faithful, his power to transform the debate by uttering something like what I've written atop this column is unique.

All of which means that if the media push this question at every opportunity, we'll find out soon enough if Christie is the real thing.

Matt Miller, a senior fellow at the Center for American Progress and co-host of public radio's "Left, Right & Center," writes a weekly column for The Post. He can be reached at mattino2@gmail.com. Follow him on Twitter at @mattmillernow.