In the election of 1912, Teddy Roosevelt stabbed his friend in the back by forming a third-party progressive party to challenge the status quo in the Republican Party.
Roosevelt would lose and his faction of progressives would float between the parties until being captured by Roosevelt's distant cousin FDR, who was a Democrat, as he pushed for the codification of progressive ideals in the New Deal.
The end result: The Republican Party, once the party of reform, would love their reform wing to the Democratic Party.