Liberal candidates retained the party's seats in Toronto Centre and Montreal's Bourassa riding, while the Conservative candidates maintained the party's dominance in Manitoba's Provencher and Brandon-Souris ridings. The Brandon win, however, was a narrow one for the Conservatives over the Liberals. The NDP pointed out that the result in Toronto Centre was its best-ever in the riding.
Celebrating the third-party Liberals overtaking the Official Opposition NDP in all four byelections, Trudeau said New Democrat Leader Tom Mulcair is different from Layton, his predecessor.
“Make no mistake, the NDP is no longer the hopeful, optimistic party of Jack Layton. It is the negative, divisive party of Thomas Mulcair,” Trudeau said in Bourassa.
Stealing a line from Layton’s famous death-bed letter to Canadians, Trudeau added: “It is the Liberal Party tonight that proved hope is stronger than fear.”
Trudeau's use of the line fired up NDP supporters, many of whom are fierce defenders of Layton and still revere him for his ability to bring the party to its best-ever electoral result.
The New Democrats' national director Nathan Rotman sent out an angry tweet.
George Soule, a spokesman for the party who's currently on leave, also reacted on Twitter.
Words used as 'political tool'
Asked in Ottawa Tuesday about Trudeau's choice of words, Mulcair exhaled and looked skyward before answering.
"That Justin Trudeau would use Jack Layton's dying words as a political tool says everything that needs to be said about Justin Trudeau's judgment and character," Mulcair said.
New Democrat MP Olivia Chow, Layton's widow, focused her reaction on Prime Minister Stephen Harper.
"I'm quite surprised that the leader of the Liberals used my late husband's words, but at the end of the day Stephen Harper is the prime minister," Chow said.
"If we are to have a better country, and certainly Canadians deserve a lot better, we need to focus on Stephen Harper. Yes, we are the party of love, hope and optimism and let's be hopeful. Let's not be fearful of each other, but let's train our eyes on the real problem, which is Stephen Harper's government."
Trudeau, however, was unapologetic, accusing the NDP of being nasty and divisive in the hard-fought campaigns, which saw all three major parties use aggressive tactics.
'Inspired by Jack Layton's legacy'
"I am, as many people are, inspired by Jack Layton's legacy and the way that he approached politics," Trudeau said.
"When you're being positive, when you're being focused on bringing people together and not playing negative politics and other people are, I don't think it's negative to highlight the fact that people are being negative around you when you're not attacking and not being negative."
But flyers used in Toronto Centre suggest the Liberals didn't stay as positive as Trudeau said.
The flyers use a photo of Mulcair from question period with the label "too angry." The attack picks up on a theme also used by the Conservatives against Mulcair.
The reverse side refers to "the NDP's radical plan for Toronto Centre."
Trudeau said the amount by which the Liberal Party increased its share of the vote shows it is connecting with Canadians "and getting Canadians once again to believe in the positive force that can be politics."
In a letter to Canadians, released the day he died, Layton touched on the optimism he seemed to embrace throughout his political career.
"My friends, love is better than anger. Hope is better than fear. Optimism is better than despair. So let us be loving, hopeful and optimistic. And we’ll change the world," he wrote.
At the time, Liberal MP Ralph Goodale picked up on some familiar words.