While I have no way of knowing if that's true, it's not too hard to take a few flaws in how our perception works[0] and a starting point to get to believing in widespread election fraud.
1. I'm a Republican because of policy X.
2. I'm a person that thinks carefully about facts and reason.
3. Trump is the Republican candidate -> President.
4. I voted for the Republican. I must have done that because of #2 (and not just #1.)
5. Trump speaks the truth - he speaks for the people, people like me.
6. Trump believes election fraud is a problem. Combine #4 and #2 and the linked perceptual flaws of selective focus, imagining that election fraud could happen, allowing myths/stories to guide my responses to the things I read... plus I'm carefully thinking about facts and reason, and I voted for Trump, and most of the people in my social network also voted for Trump... it must be the plurality of the nation. My peers are also carefully thinking about facts and reason, and I'm sure the news networks I follow do as well...
This is super simplified and skipping about a thousand steps, and yet, it's really not hard to see almost anyone getting somewhere they never thought they'd end up after years of reading and listening to mostly facts that agree with what Trump tells his believers.
That's probably easier to believe happened than "I want to be an extremist and I want to violently attack Congress when they attempt to certify an election, even though it was a legitimate election."
[0] https://www.psychologytoday.com/us/blog/pieces-mind/201208/f...