Liking a political leader and wanting to vote for him or her can be two very different things.

Take the example of Canada's three federal leaders.

Justin Trudeau's approval ratings are high and he tops the polls on who would make the best prime minister. But his chief rival on that latter question is not Thomas Mulcair, who boasts similarly impressive approval ratings, but rather Stephen Harper, who has ratings no incumbent leader should envy.

Harper's approval ratings have been relatively consistent for some time. A simple average of polls conducted since mid-May gives the prime minister an approval rating of just 34 per cent, compared to a disapproval rating of 58 per cent.

While that is an improvement on his average numbers from earlier in the year, when his approval rating was around 31 per cent, it is lower than the 37 per cent Harper was able to manage in the latter half of 2012.

It is also considerably lower than the approval ratings of his two main opponents on the other side of the House of Commons. Over the same period of recent polling, Mulcair has averaged an approval rating of 43 per cent and Trudeau 45 per cent. Their disapproval ratings, at 32 and 39 per cent respectively, are also superior.

Yet Mulcair is not as competitive on the question of who would make the best prime minister. An average of recent polls suggests about 17 per cent of Canadians would select the NDP leader, compared to 28 per cent for Harper and 31 per cent for Trudeau. And Mulcair's numbers have been worsening — he was polling at around 20 per cent earlier in the year.

That trend is somewhat contrary to Mulcair's improving approval ratings. Before the Senate scandal re-ignited last fall, the NDP leader's approval rating averaged about 34 per cent, with equal proportions disapproving or having no opinion. After the scandal broke, and Mulcair received rave reviews for his performances during question period, the number of Canadians saying they had no opinion of the NDP leader dropped by about 10 points.

Virtually all of those people who finally formed an opinion of Mulcair liked what they saw.

But that has not translated into higher support, as Mulcair continues to lag on leadership polling and his party remains stuck in third place.

Familiarity a factor, good and bad

Trudeau, on the other hand, has remained ahead on both measures despite his growing disapproval rating. His approval rating has been generally consistent since he became leader of the Liberal Party. However, in the first three months of his leadership his disapproval rating averaged 27 per cent, with 29 per cent undecided. For the remainder of 2013, those undecideds fell by about 10 points.

But the number of Canadians who said they disapproved of the Liberal leader also increased by about 10 points. Nevertheless, this has yet to hurt his party in the polls.

One factor holding Mulcair back may be the lack of familiarity Canadians have with him. A poll by Abacus Data, conducted Aug.15-18 and interviewing 1,614 online panelists, found 51 per cent of respondents either had a neutral impression of the NDP leader or did not know what kind of impression they had of him. This compared to just 34 per cent for Trudeau and 28 per cent for Harper.

The challenge for Mulcair, then, would seem to be to get more Canadians to get to know him. The polls suggest that in the past this has worked well for the Official Opposition leader, at least on a personal level. This may explain the recent NDP campaign to roll out policy proposals and to contrast Mulcair's experience with that of Trudeau.

But it may not work. The same Abacus Data poll asked respondents if Trudeau was "in over his head," borrowing an attack-ad line from the Conservatives. The survey found that a majority of Canadians said that he wasn't, or that if he was he could "learn on the job."

It would appear that Canadians are giving Trudeau the benefit of the doubt, while Harper retains a solid base of support. Unless Mulcair can turn sympathy into votes, it leaves him and his respectable approval ratings in the lurch on the question that matters most.

The Abacus Data poll asked the following questions: “Do you think Justin Trudeau ‘is in over his head', as Conservatives have been saying?” and “Do you have a positive or negative impression of the following people? Prime Minister Stephen Harper / NDP Leader Tom Mulcair / Liberal Leader Justin Trudeau”. As the poll was conducted online, a margin of error does not apply.

This article reviews trends in national public opinion surveys. Methodology, sample size, and margin of error if one can be stated vary from survey to survey.