In the summer, Mr. Trudeau and his party’s approval ratings began to recover, and the Liberals have been running neck-and-neck with the Conservatives in polling.

Mr. Trudeau’s political fate largely rests on his ability to win over fickle voters in Quebec and Ontario, the two most populous Canadian provinces. Both have large ethnic minority communities whose support has been essential for the Liberal Party, analysts said.

In majority-French Quebec, Mr. Trudeau’s Francophone roots give him an advantage, while his pro-immigrant stance as prime minister has won over many immigrants.

Then there are the young voters. Mr. Trudeau must energize them again, just as he did in the previous election, in particular those under 35, said Ms. Gainey, the former party official.

Shachi Kurl, executive director of the Angus Reid Institute, a nonprofit polling group, said progressive young voters, an important target for Mr. Trudeau’s campaign, are likely to be most offended by the new pictures and video.

Still, Mr. Trudeau wins praise as one of the most talented retail politicians of his generation and most effective when under pressure.

In an interview before the latest revelations, Stephen Bronfman, the chief fund-raiser for the Liberal Party and a member of one of Canada’s wealthiest families, recalled that at first it was hard to convince some members of the business community to embrace Mr. Trudeau, whom they regarded as a tax-and-spend liberal.

But Mr. Trudeau’s talent at connecting with an audience converted many of the skeptics, he said.

“I had chills on the back of my neck,” Mr. Bronfman said, recalling a talk Mr. Trudeau gave to a group of business people in Toronto. “It was so pure. You could hear a pin drop.”