At the same time it should have been no surprise. Trump's campaign was built on lies from the very beginning, and the media failed to call him out on his lies early enough. But more importantly, the US political debate seems to have descended into a post-truth situation, where there is no longer agreement on basic facts, like where Barack Obama was born, or who won the 2020 election.
This isn't unique to the US (the Brexit campaign being a dismal case in point), and it's not a completely new development (as a glance at the history of US election campaigns will show). But it's clearly been facilitated by allowing freedom of expression (for those who can afford it) a higher priority than public safety when the FCC dropped the Fairness Doctrine in 1987. The Fairness Doctrine might not have been sustainable in the digital age, now that everyone can become their own publisher on the internet, but at least it was a benchmark for good behaviour. Since then, the rabid right have used age-old tactics to radicalise their base and get funding to create a fact-free universe of discourse.
We in fandom had a taste of this five years ago with the Sad Puppies campaigns. Larry Correia, Brad Torgersen and Vox Day (and others) steadily pumped out lies about the Hugo awards and indeed about their own actions, and bragged about how much good this was doing their sales. Sticking to the truth was much less important for them than owning the libs. Hugo voters were repulsed by their tactics and rejected them massively. It's awful that 46% of US voters did not feel that way about Donald Trump in 2016. It's even worse that he got 47% in 2020. (Which fortunately was not enough.)
Daniel Patrick Moynihan famously said that everyone is entitled to their own opinion, but not to their own facts. That aphorism has been turned on its head by recent history. I don't know what the conclusion is. Perhaps it shows that it's always worth challenging intellectual and rhetorical dishonesty if you have the energy, including from people you normally agree with. The truth is worth standing up for.