MILWAUKEE -- Days removed from a humbling defeat in New Hampshire that stirred fresh concern about her candidacy, Hillary Clinton questioned the feasibility of the platform that has fueled Bernie Sanders' unlikely insurgency, challenging her rival during a nationally-televised debate to "level with the American people" about the true cost of his plans.
As the playing field in the Democratic nominating contest expands to a wider and more diverse collection of states, the former secretary of State argued that she and Sanders must be "held to account" for what they propose to do as president and said the numbers behind Sanders' plan for a Medicare-for-all system "don't add up."
Sanders rebutted Clinton's assertion that his plan would undermine the Affordable Care Act, President Barack Obama's signature domestic achievement, saying his life's work has been dedicated to ensuring health care was "a right for all people."
"We're not going to dismantle everything," he said.
But Clinton insisted that her vision for building on the president's health law was more affordable and more politically viable.
"We have to also be very clear, especially with young people, about what kind of government is going to do what for them and what it will cost," she said.
"Secretary Clinton, you're not in the White House yet," Sanders shot back.
The tough exchanges were proof of how much the race has changed after Sanders' big victory in New Hampshire. Clinton now faces a very real threat that she may not win her party's nomination.
The 22-percentage-point rout in New Hampshire was a wake-up call to the Clinton campaign and put Sanders in position to compete in states Clinton had appeared to own, including Nevada and South Carolina, home to the next caucuses and primary, respectively.
Clinton also acknowledged her surprising struggle to win over women voters -- particularly younger women.
"I have no argument with anyone making up her mind about who to support," Clinton said. "I just hope that by the end of this campaign there will be a lot more supporting me."
But Clinton has also sought to cast doubt on the image Sanders has cultivated of himself as a politician who refuses to follow the rules of the Washington establishment. Her campaign has noted that despite his disavowal of big donations from Wall Street, he has benefited from their support through the Democratic Party's national campaign committees.
In the debate, Clinton made a different point, defending her taking of contributions from people with ties from the financial industry by noting that President Obama had done so as well and had still pushed legislation to crack down on Wall Street abuses.
"Let's not insult the intelligence of the American people," Sanders responded, saying that corporations and wealthy people do not simply "throw money around," but spend it with a purpose.
Both candidates used their opening statements to address issues of concern to minority voters, particularly blacks, who make up a majority of voters in South Carolina.
Clinton noted that her first speech of the campaign was on the issue of criminal justice reform, while Sanders, who has said the economy and political systems are rigged, referred to "a broken criminal justice system."
While the candidates generally take the same positions on immigration, police brutality, voting rights, environmental justice and other issues of particular concern to blacks and Latinos, Clinton is far better known in communities of color, and polls suggest she holds a substantial lead over Sanders in them.
Leading up to the debate, Clinton's campaign attacked Sanders as a Johnny-come-lately on civil rights issues, saying Clinton was on the front lines of major fights while Sanders was at best an obscure backbencher.
Clinton has boosted her profile as a civil rights crusader lately by taking a leading role in demanding justice for the citizens of Flint, Mich., a low-income, majority black city whose residents have been poisoned by lead in their drinking water. Hours before the debate, the Congressional Black Caucus political action committee formally endorsed Clinton.
But Sanders makes the case that his economic proposals -- which include free tuition for public colleges nationwide, guaranteed government-funded health care and a $15 minimum wage -- would do significantly more for economically disadvantaged minorities than Clinton's more moderate plans.
In their last confrontation, which took place days before the voting in New Hampshire, the two clashed over the definition of "progressive." Clinton accused Sanders of essentially hijacking the term, by defining it so restrictively that Obama and Vice President Joe Biden would not qualify because they have accepted campaign contributions from financial interests and championed the Pacific trade deal reviled by organized labor.
Clinton demanded that Sanders explain how even he qualifies under his own definition, given his history of voting against some gun safety rules. Clinton will be looking for opportunities to return to the gun issue again.
Beyond Sanders and Clinton, the person whose presence was most felt in the early part of the debate was Obama. Clinton particularly brought up the president's name. She has made the case that she is the candidate best positioned to carry on the president's legacy.
Continuing on Obama's path appeals to many Democrats, but especially blacks. By contrast, in New Hampshire, where the electorate is overwhelmingly white, Democratic primary voters divided very closely on whether they wanted the next president to continue Obama's policies or move to more liberal ones, according to exit polling. Clinton won among those who wanted continuity, Sanders among those who wanted a more liberal turn.
Sanders has tended to waver on his allegiance to the Obama legacy, offering praise for the work the Obama administration did in saving the country from economic collapse, but also lamenting how little was achieved to stem income inequality during Obama's two terms. Sanders wrote a blurb that appears on the jacket of a recently published book about how progressives view Obama, called "Buyer's Remorse."
"Read this book," the blurb says.