You can think of the three minor candidates who were onstage at last night’s Democratic Presidential debate as ghosts, who, in addition to whatever other qualities doomed them to insignificance, represent vanished political types. Lincoln Chafee, as he noted, was the liberal Republican, a once influential, though maybe not numerous, group that was long ago expelled from its original party but has not been fully accepted by its new one. Jim Webb was the Reagan Democrat—the military-culture white Southerner who leans conservative on social issues. Martin O’Malley was the urban Catholic white-ethnic liberal, representing what’s left of the old political machines that produced the Kennedys. None of these groups could be written off in late-twentieth-century presidential politics; now, evidently, they can.

Bernie Sanders, on the other hand, was the undead: a representative of an ideology, socialism, that was buried with the Eugene Debs campaign of 1912, but now, unaccountably, has been resurrected, with “middle class” replacing “workingmen” in the rhetoric. Yes, Hillary Clinton won the debate, and yes, she will be the Democratic nominee, but the big surprise of the Democratic campaign so far has been voters’ response to Sanders. A year ago, nobody would have predicted that of the other Democratic presidential candidates, Sanders would be the one who mattered.

There seems to be more going on here than Sanders’s ability to take advantage of the atypicality of Iowa and New Hampshire, the first two voting states in the campaign for the nomination. More than the other candidates, he has a simple, clear, strong message, which he repeats constantly. The packaging—Brooklyn accent, bad hair—reinforces the sense of angry authenticity. And it’s worth noting that he’s obviously uncomfortable when forced outside the tight box of economic populism. That’s why he has trouble talking about Black Lives Matter and gun control. (Margaret Talbot wrote about Sanders’s campaign for the magazine last week.)

One aspect of Clinton’s adept performance last night was that at every opportunity, she tried to change the subject from her Democratic opponents to the Republicans. She knows they’re her real opponents, and a far more significant obstacle to her becoming President. So, on the evidence of the debate, how do her prospects look? Merely being prepared, assured, and on-message doesn’t guarantee victory. You also have to connect.

The big, obvious gap between the two parties at this moment is on non-economic issues. In the Republican debates, it has been interesting to see how difficult a time the more moderate candidates have had creating any general-election breathing room for themselves on issues like abortion, gun control, marriage equality, and immigration. Conversely, it was interesting to see last night how completely comfortable Clinton has become with what not long ago were dangerously liberal positions, even for a Democrat, on these issues. This year Clinton and her party are obviously betting that social issues will break strongly their way. If they turn out to be wrong, that will be an unpleasant surprise for Clinton.

The strong feelings that Sanders has tapped into present a greater challenge for Clinton. For one thing, the voters this year, in both parties, are in an anti-Establishment mood—that explains not just Sanders’s popularity, but also Donald Trump’s and Ben Carson’s. Clinton is part of the Establishment, and there’s no way around it. She was also the least anti-Wall Street candidate on the stage last night. It was almost surreal to see Anderson Cooper, the moderator, have to define Glass-Steagall—a Depression-era piece of financial regulation that Bill Clinton effectively repealed when he was President—because the candidates were so eager to talk about it that they forgot the first rule of debate training, which is never to get technical. Clinton noted that as a senator, she represented Wall Street, and her attempts to distance herself from it were obviously well rehearsed, but not even in Sanders’s range, emotionally.

In the Times last week, Thomas Edsall wrote a counterintuitive column arguing that the Democrats have become, if not the party of the rich, the party that has the loyalty of most rich people. Clinton would never sign on to that sentiment, but Sanders’s challenge has forced her into speaking supportively about “capitalism” and “business”—not traditionally Democratic terms—onstage. And on the Republican side, though almost everyone’s rhetoric is anti-government, we have not heard defenses of Wall Street in response to the Democrats’ attacks. The Democrats don’t automatically own economic populism in this election.

There is no chance that the Republican nominee, whoever it is, will talk like Bernie Sanders. But it’s almost certain that he will argue that, more than Clinton, he understands the behind-the-eight-ball feeling that pervades the American middle class, and propose to do a better job of fixing it than she would. Such an argument won’t necessarily come across as hollow just because it’s coming from a Republican. Bernie Sanders is getting at something powerful, which matters to a lot more people than socialists. Clinton’s biggest challenge is finding her way to a more powerful, and perhaps less prepared, way of persuading the disempowered middle class that she can be its champion.