The single payer Halloween horror
Since you brought up Paul Krugman, let's not forget one of the dumbest and most dishonest things he's ever said (and that's saying a lot): his assurances that the tales of horror emerging from socialized medicine in Britain were mere myths, unsupported by the facts. If memory serves correctly, James Taranto of the Wall Street Journal used to repeat that Krugman quote after every story about old people left to die of thirst in British care facilities, and people suffering in agony while they waited interminably for services which are readily available to Americans.
Of course it's not a "conspiracy theory" to say that single payer was the goal - it's the universal, repeatedly stated goal of every power- and cash-hungry statist on the Left. You'd have to drill pretty far down into state and local politics to find a Democrat politician who doesn't lie awake at night dreaming about it. Socialized health insurance was a brass ring they were willing to sacrifice careers to grab. Socialized medicine is the endgame of liberty, a restructuring of power that puts Big Government and its acolytes in control forever. There are a few societies beginning to awaken from the single-payer nightmare, but it's a slow and painful process that takes decades. In the United States, it would be even longer and more agonizing.
It would be a good idea for Republicans to explain why single-payer is horrible, rather than just assuming everyone with an ounce of common sense knows that. There are plenty of people, beyond the hard core of committed leftists who view it as political checkmate, who will find allure in the idea of nipping over to a government-run clinic to get all their health care for "free." There are people who like being told what to do, and how to live, particularly when confronting the expense and complexity of modern medicine. Medicine is misfortune, not a product people love to shop for on the open market. Getting sick and paying for a doctor is like getting cleaned out at the blackjack table. It's not difficult to sell government control as insulation against misfortune. That might be the most powerful appeal statists have left, now that it's transparently obvious they cannot deliver prosperity.
It's actually quite encouraging that Democrats thought they needed to use the ObamaCare Trojan horse to get there, instead of just dropping single-payer on the table in 2009. The American people are still squeamish about turning doctors into government bureaucrats. They hear enough news about how that works in practice to be skeptical, especially since another distinguishing feature of socialized medicine is special top-shelf care available only to the Ruling Class, and Americans grow weary of pampering their aristocracy. I'd also play up the pivotal role America plays in the world's medical system - we're the beating heart of innovation that cannot be replaced with a single-payer aquarium pump.
But at this point, the conservative crusade against single-payer should be easy. Just explain that it's like ObamaCare, except even worse.