OTTAWA (Reuters) - Canada's Liberals have strengthened their claim to be the main challenger to the governing Conservatives in the next general election after being thrust back into the political mainstream by a strong performance in four special elections.
While much can change in the two years before the October 2015 general election, Monday's results have given new momentum to the Liberals, led by Justin Trudeau, son of former Prime Minister Pierre Trudeau.
The ability of voters who oppose the Conservatives to coalesce around one of Canada's two main center-left opposition parties is critical if one of them is defeat Prime Minister Stephen Harper's party in 2015.
There are some deep philosophical differences between the Liberals and the New Democratic Party (NDP) on their left. But some voters are happy to pick either one as an anti-Conservative standard bearer.
The NDP vaulted into second place behind the Conservatives in the 2011 election, buoyed by support for charismatic party leader Jack Layton, who died later in the year. It was the first time the NDP had won more seats than the Liberals in a national election.
The Liberals won just 34 seats in the 308-seat House of Commons to take third place, although they have pushed ahead of both the NDP and the Conservatives in recent opinion polls.
In Monday's races to fill four vacant parliamentary seats, the Liberals held on to seats in Toronto and Montreal and leapfrogged over the NDP to come second in two Manitoba contests.
"The NDP is no longer the hopeful, optimistic party of Jack Layton," Trudeau told supporters on Monday night. Seizing a line from Layton's powerful deathbed message to Canadians, he added: "It is the Liberal Party tonight that proved that hope is stronger than fear."
The NDP ran attack ads against Trudeau's handpicked candidate in Toronto Centre, a voting district that includes both subsidized housing and some of the costliest homes in Canada. Liberal candidate Chrystia Freeland, a former senior editor at Reuters, won comfortably.
Monday's other major electoral story was the reduced Conservative vote in each race, with the party holding on to the two Manitoba seats by narrower margins than in 2011.
A scandal about expenses in the Senate, the upper house of parliament, has curbed support for the Conservatives, amid opposition accusations that Harper must have known about his former top aide's decision to give one senator the money to repay improper expenses.
Harper denies he knew about the repayment, but the affair has resonated badly on a government that came to power in 2008 promising to clean up Ottawa.
University of Toronto political scientist Nelson Wiseman said the Liberals are now clearly the main contenders to replace the Conservatives.
However, he said Trudeau's novelty could wear off in the next two years, especially if voters started to question his judgment.
"Intellectually he is a lightweight compared to Harper and (NDP leader Thomas) Mulcair, and in a debate, while we don't know if the debate will matter, they could turn him into mincemeat," Wiseman said.
(Editing by Janet Guttsman; and Peter Galloway)