This can be in any country, although Portugal is probably way too easy.
Basically, can you think of a way a particular country's political system could be developed over time to effectively swap the ideological positions of the main parties? Ideally, this would be in both an economic and a social sense, since there are quite a few examples of the former (Lange's Labour vs. Muldoon's Nats) and the latter (post-Communist parties in Eastern Europe) in real life.
Enjoy!