— The day Liberal Party leader Justin Trudeau won a majority government, he quick-stepped down the stairs of his campaign jet to the tarmac, where, as cameras whirred, he joined two aides to make a human pyramid, a huge smile lighting up his face.

It was like many of the antics he had used during a 78-day campaign to project a positive, energetic youthfulness. Trudeau hoped that attitude would captivate voters who polls showed had grown tired of Prime Minister Stephen Harper and his Conservatives.

Trudeau was sworn in on Wednesday. At 43, he becomes the second-youngest prime minister in Canadian history.

“When Trudeau won, there was a huge sigh of relief from the 70 percent [of Canadians] on the left,” said Harold Jansen, a political scientist at the University of Lethbridge in Alberta.

Now Trudeau will have to prove himself. He is a rookie who came out of third place to win an election that was more about getting rid of Harper than electing Trudeau.

After nine years of Conservative government, polls showed that more than 60 percent of voters wanted Harper gone. Jansen noted that Harper’s reclusive style grew to alienate Canadians. The prime minister rarely held news conferences and was assailed for taking positions that were well to the right of many Canadians’ views. He was accused of responding slowly to the Syrian refu­gee crisis, after announcing that the government would resettle just 10,000 over three years. He weakened environmental laws. And he was criticized for opposing a Muslim woman’s effort to wear a face veil at an immigration ceremony.

Even though Harper had won three elections, he never garnered more than 39.8 percent of the vote. He won a majority the third time out because in Canada’s first-past-the-post electoral system, his Conservatives monopolized the right, while the other 60 to 70 percent of the vote was split between the four parties that crowded the center-left. This time, center-left voters coalesced around the Liberals.

As election day neared, “Trudeau just had to show up with his pants on and he would win,” said Nelson Wiseman, a political scientist at the University of Toronto.

Trudeau has promised swift action to reverse many of the Harper policies. The day after his election, he informed President Obama in a telephone call that he intended to withdraw Canada’s half-dozen warplanes from the U.S.-led campaign against the Islamic State in Iraq and Syria. Trudeau wants to emphasize Canadian soldiers’ traditional role as U.N. peacekeepers, although he has promised to maintain about 70 military trainers to help Iraqi security forces.

He also told Israeli Prime Minister Benjamin Netanyahu to expect a shift in tone in the relationship; Harper was accused of being insufficiently attentive to Palestinian concerns. Trudeau announced plans to admit 25,000 Syrian refugees by the end of the year.

Whereas Harper pulled Canada out of the Kyoto Protocol on climate change and refused to donate to the climate fund for developing countries, Trudeau said he intends to make Canada a bigger player in the Paris climate change negotiations beginning Nov. 30.

Trudeau is largely an untested entity. He is the oldest son of the late Pierre Elliot Trudeau, one of Canada’s most famous prime ministers. Although he may have inherited his father’s eloquence in both French and English, his warmth and effusive personality are all his own.

All that aside, he is very much outside the regular political gene pool of lawyers and businessmen. He worked as a ski instructor, bouncer, actor and high school drama teacher before winning election in 2008 in Papineau, a blue-collar district in Montreal.

Four years later, he became party leader at a time when a major financial scandal had sunk the Liberals to third-party status.

Changes ahead

Among his promises are to reopen Parliament in December with Canada’s first gender-equal cabinet and initiate an economic strategy to deficit-spend the country out of the recession into which it recently plunged. He is also expected to shake up the country’s scientific and environmental policies.

Canadians have long put environmental protection at or near the top of their priorities, polls show. But scientists say that the Harper government defunded important scientific research, reducing the ability of scientists to monitor the environment. About 45 million Canadian dollars ($34 million at current exchange rates) was cut from the Natural Sciences and Engineering Research Council’s budget from 2012 to 2014.

Harper has argued that he was transferring funds from pure science to applied sciences with industrial applications. He also said spending cuts were part of an overall austerity program designed to balance the budget.

The outgoing prime minister was criticized for his tight control over government scientists’ release of information to the public. A study by the Professional Institute of the Public Service of Canada found that 90 percent of government scientists felt that they could not speak freely about their work. Foreign scientists collaborating on Canadian government projects were also compelled to sign confidentiality agreements.

In 2014, more than 800 scientists from 32 countries wrote an open letter to Harper claiming that “Canada’s leadership in basic research, environmental, health and other public science is in jeopardy.” The letter was organized by the Union of Concerned Scientists in Cambridge, Mass.

David Schindler, a professor emeritus at the University of Alberta and a former government limnologist, said the restrictions on scientists were related to Harper’s support for the oil sands industry, which had propelled an economic boom in western Canada starting in the late 1990s.

“If you are an unabashed supporter of oil sands, the last thing you want is your scientists out there saying, ‘Hey, look, we’re driving caribou to extinction,’ ” said Schindler, whose work as an independent scientist concluded that tar sands mining was causing extensive environmental damage.

Trudeau has expressed support for the oil sands industry, although he has said he will reassess government policy. He has also pledged to produce an emission-reduction program with 90 days that would include donations to the climate fund for developing countries. He plans to lead a large delegation of federal and provincial ministers to the Paris climate-change talks, as a sign of Canada’s commitment. He has also announced that under his government, scientists are free to speak to journalists whenever they like.

Meanwhile, Harper — still a member of Parliament — will have to sit and watch from the back benches as the man he repeatedly depicted during the election campaign as “just not ready” for the job takes an ax to his legacy.

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