It’s rare for a politician to switch political parties, but not all that rare. Don Riegle, who served three terms in the U.S. Senate, was originally elected to Congress from Flint as a Republican.
After six years in office, he switched and became a Democrat during the Watergate scandal. Naturally, he wasn’t very popular with his former Republican friends. But you have to say this for him. He did so more than a year before the next election.