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Democratic U.S. presidential candidates Senator Bernie Sanders and former Secretary of State Hillary Clinton wave as they arrive on stage before of the start of the PBS NewsHour Democratic presidential candidates debate in Milwaukee, Wisconsin, February 11, 2016. Image Credit: REUTERS

In what was easily her strongest debate performance in recent memory — and arguably her strongest since the campaign began — Hillary Clinton was calm, cool and collected on Thursday night.

Hillary could’ve been understandably on edge, as she was fresh off a resounding loss in New Hampshire on Tuesday and an effective tie in Iowa the week before. But it was Sanders who was oddly on the defensive despite what has been momentum in his favour, starting out the night more combative than Hillary and wasting his time on petty one-liners. (When Hillary talked about building political capital when she’s in the White House, for instance, Sanders began a rebuttal with “Secretary Clinton, you’re not in the White House yet”.)

Perhaps it was understandable that Sanders appeared to be on the defensive as the major topics for the night — race, foreign policy and relations with United States President Barack Obama — are all considered areas of relative weakness for the income inequality-focused Sanders, though the depth of his policy knowledge and ability to articulate it before audiences, particularly on race issues, has improved markedly since the campaign began.

Still, as winning over minority voters will be one of the principal areas of focus for both candidates going into southern primaries — like the one in South Carolina, and polls show that Sanders is struggling to eat into Hillary’s lead in the coming contests — expectations were high for Sanders in this debate.

And while both candidates performed well initially in talking about systemic racism and reforming the criminal justice system, it was Sanders who stumbled when a moderator asked if race relations would be better handled under him than the current president. It was a foreseeable trap — asking a white man whether he’d do a better job on race issues than the first black president — but Sanders didn’t seem to see what he was walking into.

“Absolutely,” he said in response to the moderator’s question before slipping into his classic stump speech. “Because what we will do is instead of giving tax breaks to billionaires, we are going to create millions of jobs for low-income kids so they’re not hanging out on street corners. We’re going to make sure those kids stay in school are able to get a college education.”

It was as tone-deaf a line as any all night and, worse yet, it may have reminded Hillary of another line of attack she’d prepared in advance. In an MSNBC interview earlier on Thursday, Sanders had criticised Obama’s failure to connect with Congress, saying: “There’s a huge gap right now between Congress and the American people ... What presidential leadership is about [is] closing that gap.”

From a political analyst’s perspective, it’s a completely valid criticism — but when you’re running in a Democratic primary with an extremely popular Democratic president, it is, well, a weird move.

And Hillary didn’t let him — or the audience — forget about that or other critiques of the president, pivoting near the end of evening to Sanders’ frequent criticism of Obama. “I want to follow up on something having to do with leadership” she said, “because, you know, today Senator Sanders said that President Obama failed the presidential leadership test. And this is not the first time”.

Then, without changing her even tone in the slightest, Hillary launched her most vicious attack on Sanders of the debate, running down a list of the times Sanders had called the president “weak” and “a disappointment”. She ended with, “I don’t think [Obama] gets the credit he deserves.”

The argument over Obama’s legacy is one that Hillary’s campaign has been wanting to have with Sanders for some time, and Sanders set her up for an easy hit. Viewers at home watching the candidates on a split screen could see Sanders huffing and puffing as Hillary spoke, laughing angrily to himself and scribbling notes as she spoke. He clearly hadn’t been expecting that line of attack, though he might well have anticipated it. When he finally did get time to respond, he told the woman whom he’d earlier all but accused of accepting campaign donations in direct exchange for political favours that repeating his own words “was a low blow”, indignantly and with no cool whatsoever.

It was a bad look for Bernie — whom the cameras often caught wagging a finger at the moderators while Hillary spoke — and it left him struggling to articulate the reasons for the distance between himself and a popular president, a distance he’d previously tried to wave away before when an interview Obama gave to Politico seemed to suggest that the sitting president favours Hillary over Bernie.

Throughout the debate, on practically every topic, Hillary’s cool demeanour played well. Even on the one topic that should have got under her skin: Why more New Hampshire women, particularly young women, didn’t vote for her. But she resisted the temptation to be or even sound critical. “I have spent my entire adult life making sure that women are empowered to make their own choices even if that choice is not to vote for me,” she said, adding that she hoped that they’d vote their consciences in the primary and learn more about her before the general election.

After Hillary surrogates like Madeleine Albright and Gloria Steinem made the mistake of being insufficiently deferential to younger women last week — possibly costing her at least a few votes — Hillary didn’t have a lot of room to err in her answer, and she didn’t.

It was, instead, her opponent who made the mistake — repeatedly in this debate — of being too quick to anger and allowing his feelings to affect his answers. Hillary, who can hardly express an emotion in public without her ability to lead being called into question, didn’t have that luxury, and she didn’t try to indulge in it.

For once, that was an advantage.

— Guardian News & Media Ltd

Lucia Graves is a Guardian US columnist. She was previously a staff correspondent for National Journal magazine and a staff reporter at Huffington Post.