Open this photo in gallery Ontario NDP Leader Andrea Horwath speaks to the media in Parry Sound, Ont., on Friday. Ms. Horwath started this week with a strong performance in Monday’s debate, crisp messaging and a more ambitious platform. Nathan Denette/The Canadian Press

The first two times Andrea Horwath led Ontario’s New Democrats into an election, she came off like someone who shows up ill-prepared for an exam.

Her party’s policy was flimsy, and the NDP literally wasn’t ready to get her on the road. Her attempts to sell her own merits were unconvincing, and sometimes she struggled to get information correct, as though cramming with her briefing books had fallen short.

She was readier for this spring’s campaign. She began it this week with a strong performance in Monday’s debate, crisp messaging, and a more ambitious platform that she seems excited to sell.

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Still, even her own team appears surprised by how far that strong start has got her, how quickly. Their aim for the campaign’s first leg was to avoid being written out of the story as the Liberals and Progressive Conservatives go at each other. They may have underestimated how eager many voters are for an alternative to Kathleen Wynne or Doug Ford.

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As it turns out, Ms. Horwath is the story early on. And she may be about to face the biggest test of her career: the scrutiny given someone with a decent chance of becoming premier.

If that still sounds far-fetched, based on opinion polls this week showing the NDP jumping a few points – into second place, or a tie for second with the Liberals, significantly behind Mr. Ford’s Tories – some underlying numbers point to more potential growth.

Consider a poll provided to The Globe and Mail by Innovative Research Group, which surveyed 915 Ontarians through its online panel from Monday evening after the debate through Wednesday. Beyond the NDP jumping in popular support – from 21 per cent of decided voters in April into a tie at 27 per cent with the Liberals − it found Ms. Horwath making headway in how she is perceived as a leader.

Forty-three per cent of respondents expressed a positive view of her, while 19 per cent expressed a negative one – a plus-24 favorability rating, her best since Innovative Research began tracking it four years ago, and a far cry from Mr. Ford’s minus-26 and Ms. Wynne’s minus-37. She fared better than the other leaders on who most “cares about people like me.” More unusually, for a New Democrat, she also moved (narrowly) ahead on perceived competence.

Such trends often precede movement in voting intentions. So, too, might Innovative Research’s finding that Liberal supporters were more likely to see Ms. Horwath as the debate’s winner. And the NDP was the second choice of most Liberal supporters and of the PC supporters willing to consider another party.

All this is especially worrying for Ms. Wynne’s party. But even as Liberals acknowledged it could be difficult to get out of third if the NDP is ahead of them – centre-left voters gravitating to the NDP if it has the best chance of stopping Mr. Ford – they express hope Ms. Horwath is peaking early.

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That’s a danger the NDP will live with, having never peaked at all since its one victory in 1990. But it would be easier to surge a bit later, with only enough time for voters to get swept up in positive vibes.

The NDP brand in Ontario has long been weak. And the more it competes, the more rivals will try to reinforce doubts about its seriousness, economic and otherwise.

At Friday’s northern-issues debate, Mr. Ford called the NDP radically anti-resource because of a candidate he described as an anti-mining activist. Ms. Horwath handled it fine, but it was a small taste of what might come.

The NDP did not have an easy time finding candidates for all 124 ridings, so its ranks could prove a treasure trove for opposing war rooms.

And it’s not difficult to poke holes in its platform – which involves more ambitious social spending than the Liberals have committed to, backed by taxes on the rich and corporations, alongside a dubiously feasible effort to make a partly privatized energy utility public again – even though it is more thorough than previous ones.

Fending off such attacks, if they come, will rest heavily on Ms. Horwath’s shoulders.

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Her strategists believe she is their best asset. But if she is really in the fight come the campaign’s marquee leaders’ debate on May 27, her opponents will work harder to bring out the old version of her than they did this week.

Between now and then, journalists will have the chance to test her as they travel the province on the bus with her. It’s an unusual level of access, to a leader who recently wanted any attention she could get. She may be about to get more of it than most anyone expected.