Last week I expressed hope that Mitt Romney would pick Paul Ryan as his vice presidential candidate because I thought it might provoke a more serious conversation about our nation's future. But I come today neither to praise nor bury Ryan.

Ryan belongs to a heritage in the Republican Party that goes back to Arthur Laffer, the intellectual godfather of Reaganonmics. If you remember, Laffer had his famous curve, which posited that the lower tax rates actually lead to more tax revenues by increasing economic production. This supply-side theory, which Reagan's own budget director famously derided as "snake oil," has been Republican orthodoxy ever since.

But there's always been a fatal flaw in the theory: deficits. Unlike the administrations of Reagan and George W. Bush, where exploding deficits were an inconvenient truth, Paul Ryan enters the stage as a Republican who says he will make deficit reduction a central new cause of the party. He has put forth a budget — again worth reading Ezra Klein's analysis — that not only includes massive new tax cuts, but huge cuts in social programs and future — not current — entitlements. The Romney-Ryan budget, and this will be the heart of Obama's attempted take-down of Ryan, also will explode the deficit, because, once again, the math simply does not work. You cannot cut taxes, hold current entitlements harmless, raise defense spending and balance the budget, no matter how much you cut non-defense discretionary spending. There simply isn't enough of it — less than 15 percent of the budget.

What makes Ryan vulnerable is that his plan not only perpetuates the myth of the Laffer curve, but that, unlike Reagan and Bush II, who allowed deficits to rise instead of gutting social programs, Ryan's chief approach to deficit reduction is draconian cuts in the social safety net and investments in science, education and technology. His budget leaves him and Romney wide-open to attacks that their approach is not only deeply unfair, but unwise.

But here's why I like the pick of Ryan. At least he has an idea, however misguided and derivative. Maybe we can finally have a real discussion of the Republican agenda. And maybe, too, Democrats will be forced to discuss their alternative in greater detail. Let's have it out.