Trump was way more divisive the first time and he came off like a legitimate threat (which he was), so the general opinion was to stop him and keep democracy alive. It wasn't cool to support him, and you were under way more scrutiny if you were associated with him. Chrisette Michelle's career literally ended because of it.
Then COVID happened and Trump mishandled it in every possible way. Combine that with George Floyd, everyone being inside and a renewal of racial discussions in the country, and nobody wanted Trump around anymore. Biden was seen as a breath of fresh air, someone we needed to get things back on track.
Problem is that even though Trump arguably became worse, Biden wasn't Obama in the sense that he represented a new era. He was less charismatic, not as sharp as he was in his VP years, and he was much quieter than Trump was. People started thinking he was useless and his mental decline happened rapidly.
Eventually, the same people who voted for Trump in 2016 and voted against him in 2020 (didn't vote for Biden, they just wanted Trump gone) were ready to embrace Trump again. They forgave him for everything, especially COVID because in their minds, he made them rich with the stimulus/unemployment money. Biden was seen as a senile old man and Trump was cool again. What makes it worse is younger generations openly embraced him compared to last time, which made it easier for the OG supporters to vote for him guilt-free.
It doesn't help that Kamala wasn't seen as cool and people thought she was just given the spot without earning it. Trump was going to destroy Biden. Kamala had a little spark, but it quickly disappeared because Trump was way more popular now. He wasn't seen as the boogeyman anymore. Nobody cared about his previous actions because they feel like nothing bad actually happened.
Now, you have Carrie Underwood performing at the inauguration like she's Beyoncé and still having a job on American Idol. If this was 2017, she would be forced to quit. People who were against Trump (Snoop) no longer were and didn't see what the big deal was. Podcasters took Trump in, accepted him, were in awe of him. Influencers, reaction channels, they all started making the heel turn because of the money coming in. Second term Trump is way more dangerous, but he's way more popular. And America is way more stupid because you don't have a worldwide pandemic in your face letting you know how much of a problem this guy is.