WASHINGTON -- Sen. Hillary Rodham Clinton is on the attack against her main rival, charging that Sen. Barack Obama's health plan would leave millions of Americans without medical protection while hers provides coverage to all.
The assertion, flatly rejected by the Obama campaign, rests on a pivotal difference between the two Democratic presidential candidates' health proposals. Clinton says she wants the government to require all citizens to buy insurance or face a penalty. Obama relies on a mandate for children only, and instead emphasizes ways to make coverage more affordable.
The seemingly technical distinction has launched an impassioned debate among economists, health care analysts and politicians, and has fueled a key campaign argument in early-voting states such as Iowa. It will likely receive more attention as the election season grinds ahead.
Clinton is not alone among Democrats in calling for all adults to buy insurance. Former Sen. John Edwards of North Carolina, New Mexico Gov. Bill Richardson and Sen. Christopher J. Dodd of Connecticut have included the requirement in their health plans, making Obama the most notable outlier in the party's presidential field.
Clinton is using the issue to level her sharpest charges to date against Obama.
"He's called his plan 'universal.' Then he called it 'virtually universal.' But it is not either," she asserted in a recent Iowa speech. "And when it comes to truth in labeling, it simply flunks the test."
Clinton mailed a letter to Iowa voters, over the signature of former Gov. Tom Vilsack, which says "Mr. Obama threw back talking points worthy of Rudy Giuliani or Mitt Romney" when questioned about "flaws" in his plan.
In response, Obama distributed a piece in New Hampshire that defended his health proposals and urged voters to "remind Hillary Clinton" that the Jan. 8 primary "won't be won by launching misleading, negative attacks."
But as the concept of a health insurance mandate gains currency within top ranks of the Democratic Party, the feasibility of the idea remains uncertain and its effects are unproven. As the Obama campaign points out, similar requirements in other areas, such as mandatory automobile insurance and motorcycle helmet use, never result in universal compliance.
Only one state, Massachusetts, requires residents to buy health coverage. But the rule is just kicking in, making it too soon to judge how it is working. California lawmakers are considering a similar proposal.
Switzerland and the Netherlands "are the only two countries with anything like a mandate," said Robert Blendon, a health policy professor at Harvard University's Kennedy School of Government, adding that the proposed U.S. plans differ in important ways from their European counterparts.
"We are entering some uncertain terrain here," said Jonathan Gruber, a health economist at the Massachusetts Institute of Technology who helped design the state's plan. "It is new policy-making. It's very bold and exciting."
The idea of making health insurance a requirement has grown in appeal as politicians and health advocates look for ways to cover the estimated 47 million Americans who do not have it.
But even many states with a progressive streak, such as Maryland, have not embraced a Massachusetts-style mandate. Health Care for All, a group advocating universal coverage, proposed several years ago that middle- and upper-income Maryland families be required to buy health insurance, but never extended the idea to all residents.
The group is reconsidering the concept, but has not decided whether to push for it, said its president, Vincent DeMarco.
"It's a big mistake to do a health care for all plan without requiring upper-income people to chip in," said DeMarco, who also supports a mandate on businesses. "Mr. Obama needs to do that."
The concept illustrates how the health care debate has evolved over the past 15 years, with politicians looking to avoid the "big government" label that doomed the last major attempt at reform, during the first year of Bill Clinton's presidency.
Many voters, particularly Democrats, say the affordability and availability of health care is a top concern they want to see the next president address. But while voters tell pollsters that they want a presidential candidate who supports universal health care, far fewer say they want a Medicare-style government program that replaces private markets.
So candidates from both parties are stressing individual choice and the central role of employers, who would continue to be the main providers of health insurance for their workers. Under her plan, Clinton often says, "If you like the health care you have, nothing changes."
Clinton and other supporters of a mandate say the mechanism is the only way to get close to universal coverage. One of the key target groups is young people who make enough money to get insurance where they work but don't think they need it. Those people need to be in the health insurance system, proponents say, spreading risk and sharing costs.
"There will always be, absent a mandate, some people who will fail to obtain coverage," said Mark Pauly, a health systems professor at the University of Pennsylvania's Wharton School. "People with adequate or more than adequate income sometimes do remain uninsured. It's just not fair to use, in a sense, our better charitable instincts to have them impose costs on the rest of us."
The Obama campaign has a different idea for getting those that health experts call the "young invincibles" into the system. The Illinois senator wants a rule change so that those up to age 25 can stay on their parents' policies, even if they're not in school.
There's little evidence, Obama supporters note, that a simple order would achieve the goal of providing coverage to all.
Depending on the state, anywhere from 4 percent to 34 percent of drivers do not buy auto insurance, even when their state requires it, according to the journal Health Affairs.
Stiff penalties and intensive technical work, such as linking registration, license and insurance databases, are required to reach the highest levels of compliance - which are still not at 100 percent, studies show.
Other states are watching Massachusetts to see how a health requirement works in practice.
In the past few months, about 300,000 previously uninsured residents got coverage - but most were enrolled automatically through a new program for poorer residents. The penalty for not enrolling this year is a relatively low $219, a fee that is not expected to change behavior until it increases next year.
"The real mandate kicks in next year," Gruber said.
The person arguably most responsible for establishing the policy, Mitt Romney, is not calling for a nationwide expansion. The former Massachusetts governor, now a Republican presidential candidate, says states should decide individually whether the idea is right for them.
As governor, Romney embraced the concept because it comported with notions of personal responsibility - a tenet of Republican ideology. Individuals should be responsible for their own protection whenever possible, the doctrine holds, while government could nudge them in that direction. But no Republican candidate is offering a similar argument this year.
Democratic candidates and their economic advisers agree that a mandate alone is no solution to the problem of the uninsured. Also necessary, they say, is reducing the costs of insurance, which would almost certainly require huge government subsidies for the poor. Obama says it makes most sense to focus there first.
"It would be extremely unfair to enact a mandate before we make health care affordable - which could take several years," economists Austan Goolsbee and Jeffrey Liebman, advisers to Obama's campaign, said in a memo responding to Clinton's charges. "And even once a mandate is in place, the evidence suggests that millions of Americans would need to be exempted and that millions more would not comply."
Clinton has offered few details about how the idea would work. She has acknowledged that an important lesson from her failed 1993 health reform effort was the folly of the White House writing a complex proposal and trying to persuade lawmakers to accept it. She would leave it to Congress, she said, to work out the specifics of a health care plan.
The details of a mandate are less critical than the change in thinking that such a requirement would instill, Blendon said.
"The most important thing you want to achieve is a cultural change which sort of accepts the responsibility that people have coverage," the Harvard professor said. The country must create an attitude where everyone is expected to have health insurance, he said, so "when you go into a doctor's office, they are horrified if you don't have coverage."