'If you like your health care plan, you will be able to keep your health care plan, period." The line comes from President Obama's recent address to the American Medical Association, but it could have come from virtually any public statement he's made about health care in the last two years. That is no accident. Polls show that Americans think their health care system has severe problems, enough to warrant a major change. But the same polls show that a large majority are happy with their current health care arrangements.

In other words, people want change, but, more often than not, they don't want change that will affect them. And, if you don't think such skittishness can have powerful political repercussions, ask Hillary Clinton, Ira Magaziner, or anybody else involved with the last effort to reform health care, in 1993 and 1994. The Clinton health plan would have forced most non-elderly Americans to change health insurance. In the vast majority of cases, that change would have been for the better. But it didn't make a lick of difference. With a little nudge from Harry and Louise, Americans became convinced that they had more to lose from the Clinton plan than they had to gain. And they turned on it.

From day one, Obama and his advisers have been determined to avoid that mistake. But making sure people can keep their insurance turns out to be harder than it sounds. It's been an ongoing preoccupation for staff working on reform, both in the administration and on Capitol Hill. And, while they've settled on some solutions, each one of them creates its own distinct problems. In this case, what makes reform more palatable politically also makes it worse as policy.

It might seem like letting you keep your insurance is a straightforward and, for that matter, a pretty good idea on the merits. Generally speaking, if you work for a medium- or large-sized company and can afford the health plan that your employer makes available, you are in decent shape, at least relative to other Americans. Yeah, you're forking over more and more money every year. And, if you happen to work at a company with a lot of older workers, you're probably paying more than employees at companies with younger workers. But things could certainly be worse.

How much worse? Well, you could be one of those people forced to purchase insurance as an individual customer or through a small business. If that's who you are, you're probably getting a worse deal, in good part because the overhead on the plans available to you is much higher than those offered by a large employer. (It costs an insurance company a lot more to deal with 500 individuals than it does to deal with one company that has 500 employees.) Chances are the benefits in your plan aren't so comprehensive; they may cover fewer services, stick you with higher cost-sharing, or some combination of the two. And, if you have diabetes, survived cancer, or even have nasal allergies, you might not be able to get coverage--at least not at rates you can afford---because of preexisting conditions.

Worst of all, even if you have affordable coverage, it may not be that reliable. Some carriers that serve people like you have a certain fly-by-night quality to them. You're far more likely to discover one day that your health-insurance company has stopped offering coverage in your community--or, in some cases, that it's not even a licensed insurer. Since you don't have a vast, experienced human resources department negotiating rates and benefits on your behalf, you might discover that the policy you've bought doesn't actually pay for the medical services you need--quite possibly only after you've received those services and the hospital bill has arrived in your mailbox. Or you might file a large claim and learn that your carrier has canceled coverage retroactively, because, somewhere in your medical records, it found what it considers evidence of a preexisting condition.

Insofar as today's reforms strive to reorganize the insurance market, it's primarily to benefit people like you. And the idea here is pretty straightforward: to create some kind of marketplace where you, as an individual or small-business employee, can choose from among quality insurance plans the same way that an employee of a large company can. The proposals working their way through Washington right now would call these marketplaces "exchanges." In Massachusetts, a state that created such a marketplace on its own, lawmakers called it the "connector." The basic idea is the same, though. Insurance sold through these marketplaces must include a defined set of benefits and be available to all people, at one price, notwithstanding pre-existing medical conditions. Tight regulations prevent carriers from using loopholes to withhold payment or cancel coverage. People who buy coverage through the marketplaces are also eligible for subsidies to defray premium costs, depending on their incomes.

But this is where things start to get messy. Really messy. If reform sets up a marketplace where literally anybody can get insurance, some people are going to start rethinking their coverage decisions. If constructed properly, the marketplace will offer more insurance choices than even larger employers do today. Coverage in the marketplace will probably be more reliable, too, since plans won't come and go as quickly as they do when employers are offering them. Subsidies within the marketplace will make its offerings attractive, maybe very attractive, to workers with lower incomes. And, if the marketplace includes a public insurance option, that too could attract interest--particularly if, as many experts believe, public insurance can offer the same benefits for less money.

Absent additional policy changes, people who now get employer coverage might decide to drop it and instead get insurance through the marketplace. And--again, if nothing else changes--employers might start making different decisions, as well. Think for a second why employers offer their workers coverage in the first place. One big reason is that the workers demand it. If workers aren't demanding it--or, at least, if they aren't demanding it as strenuously--employers might not be so eager or willing to provide it. Put it all together, and a substantial number of people might end up moving from employer coverage into the marketplace, in some cases because employers aren't offering insurance anymore.

To be clear, many of these people will be changing insurance because it's something they've opted to do, on their own. That's perfectly consistent with what Obama, and other reformers, have said. And, by any reasonable standard, most of the people changing plans will be better off--a lot better off. But that doesn't mean it's what voters want to hear right now or that opponents of reform won't scream about all the people "losing" their coverage.

Within the administration and on Capitol Hill, the architects of reform understand this. And, so far, policymakers seem inclined to tilt reform in ways that will discourage massive shifts out of existing employer plans. One way of doing this, likely to emerge in the Senate's legislation, is to restrict access to the marketplace. Here's how it'd work: If you have access to coverage through your employer, and if you're making enough money that you don't need subsidies, then the marketplace would be off-limits to you. Wonks call this creating a "firewall."

The trouble with this solution is that, if your employer decides to offer some kind of coverage and you're too affluent to qualify for subsidies, you're obligated to buy it--even if you think you'd get a better deal through the marketplace. You might not be pleased about that if, say, your employer offers only one or two choices. You might be particularly incensed if you wanted a public insurance plan and there was one available in the exchange.

Another way to reduce the migration of people out of employer plans is to simply make the offerings in the marketplace less financially appealing. After all, if moving into the marketplace won't save you money, you're less likely to switch. This can be done by reducing the subsidies available through the marketplace (something the Senate is already on the way to doing, mostly for the sake of keeping the price tag of reform low). But this change, too, has the consequence of making reform less appealing from a policy standpoint, since it means fewer people will be getting financial assistance to help pay their insurance bills--even though, arguably, many of them could really use the help.

For either approach to be truly effective, government must take another step: It must require that all employers either provide their workers with coverage or pay a financial penalty. The "employer mandate," as it's known, is probably the single most powerful safeguard against employers dropping their plans. And it's very much a part of the emerging congressional plans. But the mandate's effectiveness will depend, in part, on how steep the financial penalty is. And, as it is, employers and their lobbyists are protesting the requirement, claiming that it will impose an onerous burden, particularly on smaller businesses that don't provide coverage now.

In an ideal world, the best approach would to be to admit that promising everybody the opportunity to keep their coverage, as Obama has done, is just not that advisable. A better promise would be that government won't force anybody to drop good coverage--that the relatively modest number of people switching insurance will be making a change for the better. There are signs that the House legislation is at least moving in that direction, since it seems to have a more porous firewall--and an apparent commitment to high subsidies.

Such an argument would be paternalistic. Government would, in effect, be defining "good insurance." But Social Security has a similar rationale; the government is effectively defining an appropriate level of personal savings. Nevertheless, the program has somehow proven enormously popular and successful at achieving its primary goal of alleviating poverty among the elderly.

Embracing this argument would also mean telling some people with insurance that their world is going to change. But Obama--or any of his allies--can say honestly to those people that change is coming anyway. As proof, they can point to the aftermath of Clintoncare, when all those people who turned against the plan ended up enduring radical changes in insurance anyway. It happened because employers, buckling under the burden of employee-benefit costs, decided to make changes on their own. They moved everybody into managed-care plans--which, as it happens, is precisely the prospect that scared so many people about the Clinton reforms.

Today, health care costs are out of control once again. If reform fails, employers will be making changes--drastic changes--to the kind of coverage they offer employees. Some will dilute their benefits; some will stop offering them altogether. Obama himself made this point during his recent televised town hall, which suggests he understands what's really going on. The majority of Americans might prefer to leave their insurance as it is, but that's not really an option. The question is whether it transforms into something better--or something worse.

Jonathan Cohn is a senior editor at The New Republic.