Clinton didn't just stake her claim for Obama's mantle, she proved she's willing to brawl for it. Sanders, meanwhile, showed he's getting more comfortable being the liberal that liberals always hoped Obama was at heart. And he made it clear he's not a fan of Henry Kissinger.
She succeeded, highlighting Sanders' 2011 musings about a liberal primary challenger to Obama and questioning Obama's commitment to the progressive cause.
That, Clinton said, is "the kind of criticism that we've heard from Senator Sanders about our president I expect from Republicans. I do not expect it from someone running for the Democratic nomination to succeed President Obama."
She also accused Sanders of straying out of the bounds of intra-party policy disputes.
"You know, senator, what I am concerned about is not disagreement on issues -- saying that this is what I would rather do, I don't agree with the president on that," Clinton said. "Calling the President weak, calling him a disappointment, calling several times that he should have a primary opponent when he ran for re-election in 2012, you know, I think that goes further than saying we have our disagreements."
The attacks frustrated Sanders enough that he at one point said that her questioning his loyalty to the President was a "low blow" and shot back: "One of us ran against Barack Obama. I was not that candidate."
But he also didn't shy away from criticizing the President's record. He said that Obamacare's reliance on private insurers gives that industry enormous influence in politics. And he criticized the Dodd-Frank financial reforms. "My view, it doesn't go anywhere near far enough," Sanders said.
Fighting for African-American voters
As the campaign transitions from mostly-white Iowa and New Hampshire to Latino-heavy Nevada and African-American-dominated South Carolina, both candidates were focused from the outset on courting minority voters.
For Clinton, it was about hitting point-by-point challenges confronting minorities.
For Sanders, it was an opportunity to hit his core argument that soaring income inequality is the injustice at the root of all of America's problems.
"We can talk about it as a race issue, but it's a general economic issue," Sanders said.
Clinton, meanwhile, was aiming to hit a much broader issue set -- and made that clear from her opening statement.
"I want to go further. I want to tackle those barriers that stand in the way of too many Americans right now. African-Americans who face discrimination in the job market, education, housing, and the criminal justice system," she said.
She also name-dropped South Carolina Rep. Jim Clyburn when calling for more federal money to be pumped into persistently poor communities. Clyburn wasn't among the members of the Congressional Black Caucus who endorsed Clinton earlier Thursday, and he plans to endorse a candidate soon, but Clinton couldn't wait. She needs African-American voters to get behind her now.
Revolution vs. reality
The last few Democratic debates have settled into a consistent pattern: Sanders simplifies everything, and then Clinton explains, in detail, why he's wrong.
Clinton can win every argument, or blur their lines, saying "we agree," but lose a debate. And it's largely because she feels constrained: Clinton is presenting herself as someone who can accomplish things in the real world, while Sanders is selling a vision.
She challenged Sanders specifically on his implication that Clinton is part of a political establishment corrupted by campaign contributions, noting that Obama "was the recipient of the largest number of Wall Street donations" in history.
Sanders said he didn't think anyone would be fooled.
"Let's not insult the intelligence of the American people. People aren't dumb. Why in God's name does Wall Street make huge campaign contributions?" he said, chiding: "I guess just for the fun of it, they want to throw money around."
But Clinton at the end found a line that may work and could be featured on the trail and in future debates -- dismissing Sanders as a one-note candidate.
"I am not a single-issue candidate and I do not believe we live in a single-issue country," she said.
Sanders throws shade
Remember when, in the heat of the 2008 primary, Obama looked at Clinton mid-debate and said, dismissively, that she was "likeable enough"?
Sanders had his "likeable enough" moment Thursday night.
It came after Clinton discussed her ability to pay for $100 billion in new policy proposals, saying that, "I think once I'm in the White House, we will have enough political capital to be able to do that."
Sanders shot back: "Secretary Clinton, you're not in the White House yet."
Passive-aggressive as it was, it showed Sanders' increasing willingness to mix it up with Clinton. Even in the last debate, under a constant barrage of attacks from Clinton, Sanders seemed unwilling to deliver such a personal one-liner.
Clinton, meanwhile, had clearly dialed back her tone, dropping the shouting and lessening the tense exchanges with the Vermont senator, while talking more to the audience.
Why the exchange about Henry Kissinger mattered
Clinton's fluency on foreign policy has long been a strength Sanders can't possibly match. So over and over, he's leaned on a single comeback: She voted to go to war in Iraq in 2002 and he voted against it.
On Thursday night, Sanders had a second she's-for-it, I'm-against-it play: Henry Kissinger.
He attacked Clinton, out of the blue, for having touted the mentorship of Kissinger, a Republican former secretary of state under Richard Nixon hated by liberals for his role in Vietnam, Cambodia and elsewhere.
"I am proud to say that Henry Kissinger is not my friend. I will not take advice from Henry Kissinger," Sanders said.
Clinton, looking a little surprised, had a ready comeback that cast doubt on Sanders' qualifications on foreign policy, saying: "Well, I know journalists have asked who you do listen to on foreign policy, and we have yet to know who that is."
But the two talked for a surprisingly long time about Kissinger and his record.
Clinton praised Kissinger, saying that "his opening up China and his ongoing relationships with the leaders of China is an incredibly useful relationship for the United States of America," no matter what anyone might think of the 92-year-old Kissinger.
But Sanders whacked at Kissinger over China, saying he'd been against the country before he was for it -- specifically by advancing "the domino theory, you know, if Vietnam goes, China, da-da, da-da-da, da-da."