How drastic? According to the budget office, which analyzed the plan using assumptions dictated by House Republicans, the proposal calls for spending on items other than Social Security, Medicare and Medicaid — but including defense — to fall from 12 percent of G.D.P. last year to 6 percent of G.D.P. in 2022, and just 3.5 percent of G.D.P. in the long run.

That last number is less than we currently spend on defense alone; it’s not much bigger than federal spending when Calvin Coolidge was president, and the United States, among other things, had only a tiny military establishment. How could such a drastic shrinking of government take place without crippling essential public functions? The plan doesn’t say.

And then there’s the much-ballyhooed proposal to abolish Medicare and replace it with vouchers that can be used to buy private health insurance.

The point here is that privatizing Medicare does nothing, in itself, to limit health-care costs. In fact, it almost surely raises them by adding a layer of middlemen. Yet the House plan assumes that we can cut health-care spending as a percentage of G.D.P. despite an aging population and rising health care costs.

The only way that can happen is if those vouchers are worth much less than the cost of health insurance. In fact, the Congressional Budget Office estimates that by 2030 the value of a voucher would cover only a third of the cost of a private insurance policy equivalent to Medicare as we know it. So the plan would deprive many and probably most seniors of adequate health care.

And that neither should nor will happen. Mr. Ryan and his colleagues can write down whatever numbers they like, but seniors vote. And when they find that their health-care vouchers are grossly inadequate, they’ll demand and get bigger vouchers — wiping out the plan’s supposed savings.

In short, this plan isn’t remotely serious; on the contrary, it’s ludicrous.

And it’s also cruel.

In the past, Mr. Ryan has talked a good game about taking care of those in need. But as the Center on Budget and Policy Priorities points out, of the $4 trillion in spending cuts he proposes over the next decade, two-thirds involve cutting programs that mainly serve low-income Americans. And by repealing last year’s health reform, without any replacement, the plan would also deprive an estimated 34 million nonelderly Americans of health insurance.

So the pundits who praised this proposal when it was released were punked. The G.O.P. budget plan isn’t a good-faith effort to put America’s fiscal house in order; it’s voodoo economics, with an extra dose of fantasy, and a large helping of mean-spiritedness.