For much of Ontario’s election campaign, everything broke Andrea Horwath’s way, and she performed well enough to take full advantage of it.

Sunday evening’s leaders’ debate, the final time the province’s three major-party leaders took the stage together before the June 7 vote, was a very different story.

With her New Democrats now roughly tied with Doug Ford’s Progressive Conservatives in most polls, Ms. Horwath had a big target on her back. That made it much harder for her to rise above the fray, the way she did earlier in the campaign when Mr. Ford and Kathleen Wynne – whose Liberals are now polling third – went at each other.

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But Ms. Horwath did not adjust well to the attention that comes with having the momentum. She allowed herself to be so thrown off what worked for her to this point – when she presented herself as a sunny alternative more grounded than her unpopular opponents in Ontarians’ everyday struggles – that her party has reason to worry the race’s trajectory is about to change again.

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It was not that Ms. Horwath wasn’t able to vigorously defend her agenda; there were no deer-in-the-headlights moments one might expect from a third-party leader suddenly catapulted into first. And she managed to brush off attacks on her party’s basic competence, as when Mr. Ford went after her (and exaggerated) a basic math error in her platform, with relative ease.

But there were at least two potentially consequential ways that this version of Ms. Horwath differed from the one she has otherwise presented.

The more substantive of those, and also the more difficult for her to avoid, was ideological. While Mr. Ford’s attempts to paint the NDP as crazed socialists who would inflict economic disaster “ten times worse” than under the Liberals were so hyperbolic that they likely only landed with the PC base, Ms. Wynne had more success drawing Ms. Horwath into exchanges that may have caused her to seem more preoccupied with the concerns of unions than the broader public.

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Sure, it’s very rich of the Liberals to suddenly treat union alliances as indictments now that organized labour has abandoned them for the NDP, after big assists in previous Liberal victories. But Ms. Wynne drew Ms. Horwath into playing to her base in a back-and-forth about collective bargaining that may have sounded like another language to people not deeply invested in labour issues. And later, Ms. Horwath’s opposition to for-profit daycare centres set up a line from Ms. Wynne that could stick: “I’m looking for the fairest, most practical solution and you’re looking for the purest ideological solution.”

But the difference in Ms. Horwath’s performance that may have been more damaging, and should have been easier to avoid, was more a matter of demeanour.

Before this campaign began, her top strategists assessed that if anger was this election’s prevailing sentiment they couldn’t beat Mr. Ford, but that if voters wanted more optimism with their change they had a chance. So it could not have been their plan, after the rest of the campaign seemed to be living up to that assessment, for her to be the grumpiest person on the stage.

No, she couldn’t just stand smiling to the side this time and then come in with a clever line about being able to do better than the other two. But she didn’t have to spend most of the evening constantly trying to interrupt the other leaders with her own attacks, and either getting visibly heated or all but rolling her eyes every time they took a shot at her.

One of the debate’s telling moments came when Mr. Ford mostly ignored a question about workplace power imbalances, pegged to the wave of sexual-misconduct allegations that brought down the previous PC leader, Patrick Brown, in favour of raising unrelated NDP candidate controversies. Ms. Horwath took the bait by vigorously defending her nominees and attacking the PCs’ – leaving it to Ms. Wynne to play the role Ms. Horwath did when they debated earlier in the campaign, by turning down the temperature and thoughtfully returning to the question at hand.

It was a dynamic that seemed to have reversed for much of the night. After Ms. Horwath was widely judged the winner of the campaign’s first debate, Ms. Wynne came off on Sunday as the leader with best combination of empathy and competence.

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But then, it was easier for Ms. Wynne to do so this time because she wasn’t the focal point of attacks any more, a reflection of her Liberals running third. And given the indications so far this campaign that Ontarians have already moved on and tuned her out, even her best performance may have been too little and too late.

As for Mr. Ford, he was more confident than earlier in the campaign, with a somewhat better ability to convey an agenda of cutting Ontarians’ everyday costs. But for voters who have already decided the erstwhile front-runner doesn’t deserve to be taken seriously, his inability to go deep on several of the topics – and the other leaders repeatedly reminding viewers that the Tories still don’t have an actual platform – may have curbed his ability to change minds.

With only 10 days until the votes are counted, then, Ms. Horwath has to hope the things that broke the NDP’s way earlier are now too set to break back. It’s not exactly the outcome her party wanted, coming out of her biggest moment in the spotlight.