If I have learned anything in the last 60-odd years, it's this:
The history of human 'civilisation' is a list of one cock-up after another.
Given the choice between conspiracy and cock-up, assume cock-up. You will be right 90% of the time.
Where there is a conspiracy, the conspirators will cock it up at some point.
So, the GOP cocked up their selection process and ended up with Trump as their candidate.
The Democrats cocked up their campaign and Hillary Clinton ended up looking like she didn't give a shit because they all thought she couldn't lose against a rank outsider. Democratic voters cocked it up in 2016 because they thought the same. Republican voters cocked it up because they thought their party could control its candidate.
President Trump spent four years cocking everything up because he never had a clue what he was doing. He tried to run the country like he ran his businesses, and they didn't do that well either. Then he cocked up his 2020 campaign by telling people that if he lost, it would be because of election-rigging. That caused some Republican voters to stay at home, because why bother if it was a foregone conclusion, and pissed off enough Democrats to get them out to vote. Victory by cock-up for Biden.
And so it goes.