If the U.S. had a multi-party system, we’d be seeing the same kind electoral collapse in the country’s centrist parties and rise of populist parties of the right and left that we’ve witnessed in Italy and Germany. But because our electoral system so strongly favors two parties, this shift is happening internally to the Republicans and Democrats. A generation or more from now, our parties will probably have the same names and trace their histories back to the same heroes of the past, but their ideological configurations will probably be very different than what they were during the decades immediately following the end of the Cold War.
The transformation of the GOP into a right-wing populist party is already well underway. Partly in response, the Democrats are following suit by shifting further left. Not that either change is happening without a fight. On the contrary, just as the formation of a stable and coherent government in a multi-party system becomes more difficult when parties further removed from the center gain in strength, so the big-tent parties that prevail in two-party systems begin to buckle as those on the inside drift apart ideologically from one another. But of course the gap separating members of the same party is nowhere near as wide as the even greater chasm that separates each party from the other.