“Traditionally, the nation’s political business has been done by two parties, not three or more. We think this is as it should be. It has advantages quite apart from the obvious technical ones. Voluntary limitation in the number of parties brings pressure to bear on minority political groupings to accept reasonable compromises, abandon sectarianism, and join the viable party nearest its position. By the same token, there is pressure on the larger parties to make room for such groupings by giving sympathetic attention to their demand. The two pressures militate toward broad consensus—and, therefore, do a more harmonious, less divided society.
“On the other hand, the United States has traditionally left people reasonably free to launch so-called “third parties,” and this also is as it should be. It enables groupings that do not find accommodation in the major parties to let off steam, for one thing, and to ascertain whether they have the popular support they often claim. They are an indispensable shotgun behind-the-door, for possible use on the major parties on that day, when, by failing to heed some sizable body of opinion, they cease to perform well their traditional function. Obviously, the shotgun-behind-the-door is useless if it is understood that nobody must ever use it.”
—Wm. F. Buckley, Jr., National Review, October 3, 1956, p. 5
In Canada, we treat our “third party” political weapons differently: they’re publicly subsidized and soldier on for decades. Our shotguns lean against the kitchen table and are almost never loaded.