You’ve described Barack Obama’s election win in 2008 as “history-making, transformative”. Yes. But not everyone liked Obama; and one way of looking at Trump’s win in 2016 is that it represented a backlash against what Barack Obama represented. The anti-Trump vote in 2020 was (so to speak) a backlash against the backlash — the sorts of people who voted for Obama in 2008 came back, and in even greater numbers.