Democratic presidential frontrunner Hillary Clinton was feeling the Bern on Sunday night.

At the party’s fourth presidential debate of the 2016 season, the former Secretary of State, until recently the contest’s prohibitive favorite, directed some of her sharpest barbs yet at Vermont Sen. Bernie Sanders, her newly insurgent rival for the nod. Two weeks before the Iowa caucuses, Clinton challenged Sanders’ record on guns, his proposal to overhaul healthcare, the cost of his plans and whether he’s been sufficiently supportive of President Obama.

Sanders, who now finds himself in a dead heat with Clinton in Iowa while padding a double-digit lead on her in New Hampshire, turned in perhaps his most self-assured performance to date. The senator from Vermont built his case against Clinton in part by invoking her historically close ties to Wall Street, including the huge sums she’s collected in speaking fees from Goldman Sachs — the closest he’s come yet to a direct incrimination of her integrity.

But it’s doubtful that either Clinton or Sanders scored a decisive victory in the minds of enough voters to tip the balance of a race that remains nip-and-tuck, at least in the first two states.

Meanwhile, former Maryland Gov. Martin O’Malley, the third candidate on the stage, acquitted himself respectably but also struggled to break through in what’s now clearly a two-person contest.

Between Clinton and Sanders, it frequently appeared as if Clinton were the underdog. On healthcare, she attacked his pitch for universal coverage via expanding Medicare as potentially jeopardizing the Obama administration’s progressive gains. “We finally have a path to universal health care,” Clinton said. “We have accomplished so much already. I do not to want see the Republicans repeal it, and I don’t to want see us start over again with a contentious debate.”

Sanders objected that Clinton’s criticism was “nonsense” and “disingenuous” and argued he was only trying to carry forward the work Obama’s healthcare overhaul had started. But whatever the merits of Clinton’s attack, it proceeded from a strategic gambit to position herself as the most capable protector of Obama’s legacy — a case she needs to sell to stanch the flow of younger, liberal voters to Sanders.

Clinton doubled down on the tactic when talk turned to reining in Wall Street. There, the former New York senator is perhaps most vulnerable to an attack from the left that she’s failed to keep faith with the increasingly vocal elements of the party skeptical of the industry and its influence. But Clinton presented it as another issue on which she’s allied with Obama against an attack from Sanders. “Where we disagree,” Clinton said, “is the comments that Senator Sanders has made that don’t just affect me, I can take that, but he’s criticized President Obama for taking donations from Wall Street, and President Obama has led our country out of the great recession.”

In his retort, Sanders invoked the six-figure speaking fees Clinton has pocketed from Goldman Sachs, arguably his most pointed criticism of Clinton in any of the debates to date. But on balance — and certainly when compared to how relatively vicious Republicans have been in their debates — Sanders was mild.

It’s a funny fact of his campaign. For all the fire and brimstone of the Sanders message — animated by an indictment of a government he says does the bidding of the most moneyed industries, and organized around a call for a political revolution to upset it — the candidate himself seems oddly averse to bringing that same heat to the debate stage. At four separate points during the Sunday debate, Sanders said “I agree” to express his alignment with a position Clinton had just articulated. None of the seven Republican candidates at their most recent debate last week uttered those words a single time.

That attitude can help Sanders look more like a statesman than his rumpled mien might otherwise suggest. That was especially true on Sunday when he declined to take some bait from NBC moderator Andrea Mitchell to go after Bill Clinton’s checkered personal behavior with other women. But insofar as it’s applied to substance, Sanders’ unwillingness to throw those differences into sharper relief may ultimately hobble his surprisingly credible attempt to stop the Clinton juggernaut.