Clinton communications director Howard Wolfson disavowed the analogy leveled by Len Nichols, a health policy expert at the New America Foundation who has consulted with Clinton and other candidates on their proposals.
But the remark still reflected the emotional dispute over how best to achieve universal health care, a key concern of many Democratic primary voters.
The Obama mailer, which the Clinton campaign traced to mailboxes in North Dakota and Alaska, shows a young couple sitting at a table, appearing to puzzle over a stack of bills.
"Hillary's plan forces everyone to buy insurance, even if you can't afford it," the headline reads.
On a conference call with reporters, Clinton advisers complained the image and the message closely resembled the $100 million "Harry and Louise" TV ad campaign waged by the insurance industry in 1994 to kill the former first lady's effort to reshape the health care system. In those ads, a middle class couple sat at a table worrying about the Clinton plan's complexities and wondering if they might lose the right to choose their own doctors.
Clinton campaign policy director Neera Tanden said the mailer falsely suggests that the New York senator's plan wouldn't bring down costs. She noted that Clinton would offer tax subsidies to help pay for insurance and would seek other cost controls before enforcing a mandate to buy coverage.
Obama, Tanden said, "betrays the cause of universal health care. For a potential Democratic nominee to be attacking universal care is quite stunning."
Nichols of the New America Foundation went farther.
"I am personally outraged at the picture used in this mailing," Nichols, a supporter of the so-called universal mandate said. "It is as outrageous as having Nazis march through Skokie, Illinois."
In late 1970s, the American Nazi party won a court battle over the right to march through the predominantly Jewish Chicago suburb of Skokie, home to many Holocaust survivors. Despite their victory, the white supremacists decided to hold their demonstration in a Chicago park instead.
While both Clinton and Obama have outlined detailed plans to make health care more affordable and accessible, Clinton would require everyone to carry insurance while Obama would make enrollment voluntary. The two have clashed repeatedly over the matter, with Obama saying people cannot be required to buy insurance if they can't afford it, and Clinton saying universal enrollment is the only way to bring down insurance costs.
Obama spokesman Bill Burton responded by pointing to comments by Massachusetts Sen. Ted Kennedy, a longtime champion of universal health care who endorsed Obama earlier this week.
"It's the passion of my life, universal comprehensive health care, and I wouldn't support Barack Obama unless I was absolutely convinced that he was for universal comprehensive health care as well," Kennedy said in a television interview. "I've tried for 38 years to get the universal comprehensive health care. I've supported 12 different proposals to try to get there. Elect Barack Obama and we will get there."