The journalists Matt Taibbi and Glenn Greenwald talk about this a lot: the question of what happened with Clinton's loss, why Trump, why these shocks and why the persistent support.
The argument would be that there's a strong elitism that manifested in the Democratic Party, which abandoned some of its core Progressive principles with things like NAFTA (and the never-ending wars). H. Clinton echoed this, with a haughty campaign that called people she should be wooing 'deplorables,' skipping campaigning in key battleground states, and blaming sexism for some of her campaign failures ("it's about me") instead of self-reflection ("How could I have had broader appeal.") Even today you'll often find people reminding you that Trump appeals to people without college degrees. Outside of a pure data context, saying that over and over again suggests that somehow people with degrees are better capable of selecting the leaders of everyone, which is an extremely elitist perspective. So Trump comes along, attacks NAFTA and free trade, speaks plainly and so forth.
Was he making false promises about returning jobs overseas, helping workers and other Sanders talking points? Absolutely. But the self-reflection that needs to happen here (given the loss of two dozen House seats and numerous local upsets) is, what are we doing wrong, here.
To wit:
Exit polls, which can be unreliable, pegged his national support at 32%-35% of the Latino vote. More tellingly were results in certain counties. Starr County, Texas, the county with the highest percentage of Hispanic or Latino voters — above 95% — voted for Hillary Clinton by a 60-point margin in 2016, but gave Biden just a five point win in 2020.
Even more amazing was Trump’s performance among Black voters. The man whose 2016 message to “the blacks” was very nearly a parody of long-ago New York mayoral candidate Mario Procaccino’s pledge that “My heart is as black as yours” must have found a new way to connect. Trump doubled his support with Black women, moving from 4% in 2016 to 8%, while upping his support among Black men from 13% to 18%. Remember, this was after four years of near-constant denunciations of Trump as not just a racist, but the leader of a literal white supremacist movement:
[...]
Trump’s numbers with the LGBTQ community were a stunner also, jumping from 14% to 28%. In September, a dating app for queer men called Hornet ran a survey that showed 45% support for Trump among gay men. Ever since Trump jumped into politics, media observers have rushed to denounce any Trump-related data that conflicts with conventional wisdom, and the Hornet survey was no different. Out magazine quoted a communications professor from Cal Poly Pomona as saying, “To tout a Hornet poll as evidence of LGBTQ support for Trump is clickbaity, sloppy journalism.” Even the Hornet editor scoffed at his own poll, before it all turned out to be true in the election.
Trump even improved his standing among white women, 53% of whom were already pilloried in 2016 for voting for a man who bragged about how you “grab ‘em by the pussy, you can do anything.”
(Matt Taibbi, Which is the Real "Working Class Party" Now?, Nov 2020)