President Barack Obama has promised, repeatedly, that Americans who are satisfied with the health insurance they have today can keep it, even if Congress passes the sweeping reform program he favors.

But is it true?

In May 2007, then-candidate Obama issued a plan to change the way working age Americans get their health insurance. He claimed his approach would “build on” the employer-based system, but a more careful examination reveals it would actually be the demise of job-based coverage.

Under the Obama plan, employers would have a “pay or play” choice. They could either provide coverage directly to their workers (“play”), or they could pay a tax to the federal government to partially finance the coverage offered through a new “national exchange.” Workers getting insurance through the exchange would also have a choice. They could either select a private insurance offering — or enroll in a new government-run plan.

But the new, government-run insurance plan wouldn’t be just another offering. No, it would be a “game changer” in every sense. Why? Because the government can present the fees it will pay for medical services on a take-it-or-leave-it basis — and doctors and hospitals have little choice but to take it, lest they get shut out of the market completely. Private insurers, on the other hand, must negotiate contracts with their networks of service suppliers. Consequently, government-run insurance almost always charges artificially low premiums based on price and other cost controls that are rightly not part of a truly private-sector marketplace.

The implications of all this certainly hasn’t been lost on single-payer advocates. They see the government-run option as a way to achieve their long-standing goal — through the backdoor.

And they’re right to see it this way, as estimates provided by The Lewin Group, a health-policy consulting firm, demonstrate. According to Lewin’s analysis (summarized in a series of slides, available here in PDF format), if the government-run option pays fees as Medicare does today, scores of employers would choose to “pay” instead of “play,” thus forcing workers out of their job-based plans and into the national exchange. Once there, quite predictably, workers would end up largely in the government-run plan because it would pay for hospital and physician care at rates that are only about 70 and 80 percent, respectively, of what the competing private insurers would be forced to pay for the exact same services.

Lewin’s bottom line is thus truly alarming: They expect 118 million people would move from private coverage to government-run insurance pretty much overnight. And it would be anything but voluntary. There would be tens of millions of workers who would rather stay with their current job-based plan than sign up with the government-run plan — but they would no longer have that as an option.

President Obama thus faces a choice. He can change course, recommit himself to meeting his campaign commitment to protect current coverage, and begin working on a reform approach that doesn’t disrupt most job-based arrangements. Or he can continue on his current course, which would lead to massive upheaval and a clear break with what he promised voters. He can’t do both.

[Cross-posted at the Corner]