Paul Ryan’s speech Wednesday night may have accomplished one good thing: It finally may have dispelled the myth that he is a Serious, Honest Conservative. Indeed, Mr. Ryan’s brazen dishonesty left even his critics breathless.

Some of his fibs were trivial but telling, like his suggestion that President Obama is responsible for a closed auto plant in his hometown, even though the plant closed before Mr. Obama took office. Others were infuriating, like his sanctimonious declaration that “the truest measure of any society is how it treats those who cannot defend or care for themselves.” This from a man proposing savage cuts in Medicaid, which would cause tens of millions of vulnerable Americans to lose health coverage.

And Mr. Ryan — who has proposed $4.3 trillion in tax cuts over the next decade, versus only about $1.7 trillion in specific spending cuts — is still posing as a deficit hawk.

But Mr. Ryan’s big lie — and, yes, it deserves that designation — was his claim that “a Romney-Ryan administration will protect and strengthen Medicare.” Actually, it would kill the program.

Before I get there, let me just mention that Mr. Ryan has now gone all-in on the party line that the president’s plan to trim Medicare expenses by around $700 billion over the next decade — savings achieved by paying less to insurance companies and hospitals, not by reducing benefits — is a terrible, terrible thing. Yet, just a few days ago, Mr. Ryan was still touting his own budget plan, which included those very same savings.

But back to the big lie. The Republican Party is now firmly committed to replacing Medicare with what we might call Vouchercare. The government would no longer pay your major medical bills; instead, it would give you a voucher that could be applied to the purchase of private insurance. And, if the voucher proved insufficient to buy decent coverage, hey, that would be your problem.

Moreover, the vouchers almost certainly would be inadequate; their value would be set by a formula taking no account of likely increases in health care costs.

Why would anyone think that this was a good idea? The G.O.P. platform says that it “will empower millions of seniors to control their personal health care decisions.” Indeed. Because those of us too young for Medicare just feel so personally empowered, you know, when dealing with insurance companies. Read on...