(FORTUNE Magazine) – Quick: whose prescription drug plan for seniors was bigger, the one Al Gore proposed in 2000? Or the one passed this year by George W. Bush and the Republican Congress, which Democrats blast daily as an inadequate sham?

If you guessed Gore, you're rational but wrong--and you haven't begun to grasp the surreal politics of Medicare. Gore's plan would have spent about $300 billion over ten years. The plan Bush recently signed into law will run to more than $500 billion over ten years. Yes, there are differences in the fine print (and further tweaks of this year's reform, especially as regards drug pricing, seem inevitable). But Bush's plan offers much more to seniors than top Democrats called for a few years ago.

The fight over the new drug bill is less about drug money for seniors than it is about denying Bush the "compassionate" image that's essential to his appeal to swing voters. Usually that image deserves to be exposed as a marketing hoax--as with the President's "no child left behind" education bill, which leaves millions of (mostly poor) children behind. But on Medicare, Bush and the GOP have ponied up some serious money.

That makes the Democrats' smear campaign a little harder to square with Democratic philosophy. From John Kerry on down, every Democrat able to call a press conference has denounced the law. Their venom today is directed toward the new drug-discount cards (offered as an initial step until the full program begins in 2006), which Democrats slam as confusing and even fraudulent.

But "their opposition seems insane," says Jeff Lemieux, an economist who runs the useful policy website centrists.org. "A Martian would be confused about what it means to be a Democrat." After all, the drug cards cost only $30 but offer low-income seniors $600 in assistance and access to discounts that could be worth much more. All those competing cards may briefly baffle seniors, but as Lemieux points out, with free money for needy grandparents on the table, "what's not to like?"

To be sure, it was Republicans who perfected health-care demagoguery during the war over Bill Clinton's health reform in 1994. Clinton's plan may have been too complex, but it was never the "socialized medicine" it was made out to be. The paradox is that Margaret Thatcher would have been tossed from office if she had proposed anything as radically conservative as Clinton's health plan--which still left many people uncovered and let private docs deliver the care.

So today's Democratic attack is pure payback. And effective payback too: Political pros agree that Democrats have thrown so much mud at the bill so fast that it's stuck, meaning Bush will get little boost this fall from passing a plan nearly twice the size of Al Gore's.

But the episode also illustrates a rule of politics: Never let the other guy steal "your" issue. Daniel Patrick Moynihan captured that timeless dynamic in a 1973 book on the battle over Richard Nixon's Family Assistance Plan, when Nixon (whom Moynihan was advising) leapfrogged Great Society Democrats by proposing a guaranteed income for the poor. "Nixon had proposed a measure of which even the most liberal Democrats had scarcely dared to dream," wrote Moynihan. "Of a sudden they found themselves behind. Behind Richard Nixon!" Of course that was intolerable, and so Democrats conspired to kill the thing.

Depressing? Perhaps. But this combat for credit is democracy's way of slouching toward progress. Nixon's failed plan eventually became the Earned Income Tax Credit, which now gives $35 billion a year to poor workers. Today Bush's drug bill means that everyone agrees that struggling seniors deserve some financial help with their meds. For all their rage on the stump, Democrats plan to mend Bush's bill, not end it.

Republicans who now feel that no good Medicare deed goes unpunished may find cold comfort in knowing they could be political casualties on America's long road toward a more decent society. But they know as well as anyone that in this political season it's nothing personal. Strictly business.