Extreme partisan polarization in US politics is normal; people just forgot because of the long New Deal + Civil Rights realignments of 1932 to about 1994, which resulted in an unusually long period where the (still very strong) ideological polarization in our political system did not cleanly map to the divide between the two major parties. The era of “bipartisanship” wasn't free of ideological divides (civil rights, anti-war movement, etc.) its just that those divisive issues cut across the parties.