The only "switching" of political Parties was when the Democrat Party switched to the Socialist Party.
Norman Thomas, six time Presidential Candidate of the American Socialist Party, explained it best:
“The American people will never knowingly adopt socialism. But, under the name of “liberalism,” they will adopt every fragment of the socialist program, until one day America will be a socialist nation, without knowing how it happened. I no longer need to run as a Presidential Candidate for the Socialist Party. The Democratic Party has adopted our platform.”