The Canadian Model
Wendell said:
Would it happen like that?
Happened in Canada.
The Liberal Party is the Natural Governing Party. They position themselves in the centre or centre-left but have no real ideology to speak of. What they deftly do is steal from and vilify the other parties, and will lurch to the left or right depending on public opinion. The ultimate "big tent" party. Since WWII the "Grits" have won 12 elections.
The Conservative Party is a right-wing ideological party that can't decide whether or not to move to the centre and fight the Liberals on their home turf. Can occasional be called on to form a government when the Liberals get truly out of line. The "Tories" have 6 election wins since WWII, but nearly ceased to exist after the greatest collapse in the history of parliamentary democracy in 1993.
The New Democratic Party is an unreformed socialist party that would fit in with pre-Blair Labour, or older versions of the German SDP or French Socialists. Have never won an election, but when Canadians want to move to the left, they elect a few more NDPers and the Liberals either respond or are reduced to a minority where the NDP can extort policy changes for its support.
I would be very interested to see this situation arise in the US. A Centrist party that has a near-monopoly on power (call it the Republicrats). A rightist party that is the perennial opposition (Reformed Dixiecans), and a leftist fringe that is a useful protest vote (DemoGreens).
Or judging my the rise of The Right(tm) in America in last 30 years, maybe the “centre” party would be more centre-right, the main opposition would be on the left, and the loony fringe would be on the far right. Seems likely these days, as the Republicans seem to be just that tiny bit more popular to squeak out election when it counts (2000, 2002, 2004), relegating the Dems to opposition for the foreseeable future. Now you just need a threat on the GOP’s right flank...