He was more lucky than unstoppable. What he really had working in his favor was eight years of Obama in the White House, though he probably would have lost to Obama if the 22nd Amendment didn't exist. Trump was, and still is, an enigma in American politics that was difficult to cover in the media and difficult to run against. I still say that Trump was swept into the Presidency by virtue of a perfect storm. Remove one or more things that he had in his favor and he would have lost to almost anyone.
This. There were dozens of factors that propelled Trump to victory; some of his own making, others that were the result of his opponents' failings, and still others that were just...random.
Speaking to Trump's lingering popularity vs. growing unpopularity with WWC voters, I can really only speak from personal experience. Southeast Baltimore County is "Trump Country" in that it was the backbone of the Democratic Party in the County for generations when Bethlehem Steel was the region's economic driver, but swung aggressively towards Trump. What's more illuminating is that it's General Assembly and County Council delegation swung from 100% Democratic to 100% Republican in 2014. The sort of Republicans who won were Trump-esque, only pre-Trump! Retired steel workers and police officers, and community association leaders angry at an influx of Section 8 housing replaced many career-office holder Democrats. That election, combined with Trump's, leads me to this not especially revolutionary theory:
White working class voters want outsiders who listen, or at least appear to listen, to their anger. This can translate to pandering to racism and xenophobia, like Trump has, or pushing for economic policies that will empower those communities, without talking down to them or just yelling "job training" over and over. Democrats can and must do this, both for their own electoral benefit, and for the sake of those very communities.