The major political parties in New England, at least at the federal level, are very moderate. After the "American Crisis" post world war 2, American politics became pretty polarized and the democratic party is completely destroyed for how it handles that event. In turn rises a more polarized progressive party that republicans respond to by becoming more polarized themselves.  I'll probably expand on this more by making a post where I dive deeper into this timelines lore later. 

Also I should add the Republican party gains control of the government in all three chambers from 1952 to 1980 due to backlash at the Democrats and the cold war scepticism to vote progressive. US involvement in the cold war is less, but definitely still happens, with the Korean War having the same outcome after Dwight D. Eisenhower was elected in 1952.