Hmm, I think this polarization and ultra high partisanship has gone to the heads of both major parties. Being a numbers guy, I thought to look at the average approval given to each president by the opposing party.

Trump 8% by Democrats so far.
Obama 15% by Republicans for his two terms/
G.W. Bush Second term approval by Democrats 11%. With 9-11 happening Bush's first term approval was 40% by Democrats. Prior to 9-11 Bush's approval by Democrats was 26%.
Bill Clinton averaged 33% approval by Republicans
G.H.W. Bush averaged 35% approval by Democrats for his 4 years.
Reagan 34% for both terms by Democrats.
Carter 32% by Republicans for his single term.
Ford 35% by Democrats for his little more than a year in office.
Nixon 42% for his first term by Democrats, 15% for his Watergate shorten 2nd term.
LBJ 44% by Republicans
JFK 48% by Republicans
Eisenhower 52% by Democrats

So prior to G.W. Bush all previous president had an opposing party approval of at least in the 30's with IKE, JFK, LBJ and Nixon's first term, above 40%. It seems to me, numbers wise the polarization and ultra high partisanship we have existing today between the two major parties began with and during G.W. Bush' presidency.

I think that during IKE's, JFK's, LBJ's and Nixon's first term, their high opposing party's approval rating can probably be traced to an era when both major parties had their conservative and liberal wings. Prior to the shedding of their unwanted wings. Then for the president's in the 30's, each party still had a large share of moderates which each party began getting rid of in the early 2000's. This coincides with party affiliation and the rise of independents which the more moderate factions have become.

From IKE through Nixon's first term, the two major parties share of the electorate ranged from 75-80% with independents making up between 20-25%/ Beginning with Nixon's second term until G.W. Bush the two major parties averaged between 65-70%. Beginning in 2005 the share of the electorate between the two major parties has dropped to between 55-60% with independents climbing to a high of 40% today. This coincides with the Republicans moving to the right and the Democrats to the left of the political spectrum.

Which brings me to an old saying during Eisenhower era. Who exactly said it, I don't know, but it stuck in my mine. When the question was asked what the Republican Party believed in as to the GOP being known as the conservative party even back then. The answer was, the same as the democratic party, only a little bit less. Perhaps back then there really wasn't that much difference between parties, ideological wise that is. There probably was much more differences in the Democratic party with their southern conservatives and northern liberals than between the Democratic party and the Republican party as a whole.

Something to think about.
It's high past time that we start electing Americans to congress and the presidency who put America first instead of their political party. For way too long we have been electing Republicans and Democrats who happen to be Americans instead of Americans who happen to be Republicans and Democrats.