Welcome to the forum! Nice list though I'm wondering how the Republicans, after not having won an election in 48 years, manage to come back in 1968. Thank you for the warm welcome
I'll explain it in depth when I write the timeline, but simply but, Truman's and Kennedy's administrations were more 'Progressive' than the Coalition would've liked, and therefore the Progressive party effectively collapsed. The more conservative members of the party (i.e. the interventionist wing), decided to start up the Republican party again with conservative members of the Coalition.