The exact same thing happened in Australia last election. As the Conservative party became more fascist and mentally ill, voters shifted to the Labour party moving it from center-left to more corporate-whore center-right, and the Labour voters in turn shifted to vote for the Greens or other socially/economically left independents.

This isn't necessarily a good thing though. The law of averages means the corporate-whore parties maintain a majority, and continue the proto-fascist march and neoliberal economic collapse.