Clinton, the national front-runner, derided as impractical Sanders' ambitious aim to replace the country's existing employer-based system of health insurance with one in which the government becomes a "single payer," providing coverage to all.
What this is really about is not the rational way to go forward," Sanders said as he responded to Clinton's argument that his healthcare plans would reignite a divisive political battle. "It's whether we have the guts to stand up to the private insurance companies."
A news report out Saturday claims that two doctors who met with Clinton during the 1993 health reform debate say she agreed that single-payer health care would be good for Americans.
Clinton urged a less-sweeping action to build on President Barack Obama's healthcare law by working to further reduce out-of-pocket costs and control spending on prescription drugs.
"We have the Affordable Care Act," she said. "That is one of the greatest accomplishments of President Obama, of the Democratic Party, and of our country."
In expressing that support, Clinton again cast herself as the natural successor to Obama and accused Sanders, until recently an independent, of being an unfaithful ally of the administration.
It's a strategy aimed at locking down Democratic primary voters, particularly minorities, who make up a huge swath of the party's base and remain devoted to Obama. But it's a riskier approach in a general election, where as her party's nominee, Clinton would have to woo voters who question whether they feel more economically secure after Obama's eight years in office.
Sanders dismissed the idea that he'd endanger Obama's hard-won victories, insisting: "No one is tearing this up. We're going to go forward."
Grassroots enthusiasm for Sanders' outsider candidacy and his unapologetic liberal message has imperiled Clinton's lead in Iowa and expanded his advantage in New Hampshire.
Clinton also rapped Sanders for voting repeatedly with the National Rifle Association while in Congress, welcoming his weekend reversal to support legislation that would deny gun manufacturers legal immunity. She rattled off a list of provisions that she said Sanders had supported in line with the NRA.
Sanders, in turn, said Clinton's assertions were "very disingenuous" and pointed to his lifetime rating of a D- from the NRA.
The debate over gun control took on a special importance given the event was just blocks from the Emanuel African Methodist Episcopal Church, where nine parishioners were killed during Bible study last summer. Clinton has made the issue a central theme of her campaign, citing it as one of the major differences between the candidates.
The third participant in the debate, former Maryland Gov. Martin O'Malley, tried persistently to insert himself into the conversation, hoping to boost his poll numbers out of single digits. But it was tough for O'Malley to stand out.
When the conversation shifted to fiscal responsibility, O'Malley said his time in Maryland made him the only person on stage to balance a budget. Sanders—an ex-mayor of Burlington, Vt.—quickly interjected, "I was mayor for 8 years, I did that as well."