Liberals usually live in fear of them, and now the Bloc Québécois is running scared.
Vote splits: They are a determining feature in any multi-party parliamentary system, and they drive election losers crazy.
The slicing and dicing of the electorate starts to fill the air like a seasonal allergen right around the two-thrids point of every federal election campaign. The NDP's rise in mid-campaign polls usually triggers another round of New Democrat-bashing by Liberals. And like spring pollen, the NDP vote usually falls back to earth.
This time, Gilles Duceppe first betrayed his nerves over the pesky rise of the New Democrats under Jack Layton - the Bloc Québécois Leader's workout buddy during parliamentary sessions.
Ditching his usual policy of never commenting on polls, Mr. Duceppe said this week that recent surveys showing the NDP catching up to Liberals and Conservatives "is a troubling trend, not so much for the Bloc as for Quebec. ... It favours a Conservative majority."
It wasn't always this way. In the 1990s, a divided right was driven to distraction by vote splitting. Jean Chrétien exploited the existence of two conservative parties to win massive majority governments that went far beyond his actual popularity.
The splits now mostly stalk the centre and left parties, producing a series of minority governments for the now-united Conservatives.
In recent campaigns, it was Liberals who launched the fear campaign to bring the NDP back down. A couple dozen traditional Liberal bastions in suburban Toronto provide the clearest examples of what's at stake. In riding after riding, Liberals won in 2008 by margins that could easily evaporate if the rise in NDP popularity holds (which it usually does not.)
In Mississauga South, to name one, Liberal Paul Szabo won by 5 percentage points over a Conservative. A strong showing by the New Democrats, who only received 8 per cent of the vote last time, could put Conservatives over the top. Similar calculations can be made in ridings in Winnipeg, the Atlantic provinces and many other places.
The math gets more complicated in Quebec, where the rise of the NDP comes from declines in support for both the Liberals and the Bloc.
In a handful of ridings in Quebec City and scattered in rural areas of the province, Conservatives do stand to at least hold and maybe gain seats if the NDP bleeds Bloc support.
In Montreal, it gets trickier. In immigrant-heavy ridings like Justin Trudeau's Papineau, the Bloc and Liberals can both lose votes to the NDP. In a more francophone and nationalist riding like Ahuntsic, it's left-leaning Bloc voters who are more likely to wander.
In the suburbs of Vancouver, NDP support could knock off Liberals, too. But in British Columbia, where polls have fluctuated wildly, the NDP is positioned to take some races - not just act as spoiler. That's if they can hold on through the coming assault.