Trump's tribal mentality has upped the tribalism on the Dem side as well, and the Dem tribe now includes socialists and proponents of open borders, which were never mainstream Dem positions before.
Again, I don't think you've made a convincing case that Trump
caused the tribalism on the Democrat side, or the mounting radicalism. I think it was already there, and had been accelerating since Obama staked out positions to Hillary's left in 2007-2008. In fact, you might have the causation backwards, in that the increasing Democrat radicalism during the Obama years is what prompted so many Republicans to support the more confrontation approach of Trump in 2016.
Occupy Wall Street was a pre-Trump movement that would have been condemned by most Democrats 20 years ago. Instead, it was either crickets or active support. Opposition to gay marriage went from being the position of both Obama and Clinton in 2008, to being a flat disqualifier on the Democrat side. Again, pre-Trump. Obama went from saying in 2010 that he had a Constitution obligation to enforce immigration laws, to doing a 180 in 2014 and implementing DACA and DAPA. Pre-Trump. And Bernie Sanders, an avowed socialist, made his mark by attacking perceived moderates
in the Democrat party, not by going after Trump. Sanders shocking rise had nothing to do with Trump (who was just one of many GOP candidates at the time), and everything to do with radicals already in the Democrat party, or young people gravitating towards his ideas.
@Jazzhead