Maybe I just don't get into the weeds on this as much as other people, but where Trump seems to differ is in calling it outright fraud whereas others use language of disenfranchisement (democrats) and preventing improper voting (Republicans). Both sow distrust in an election, but differ in the degree and kind of distrust in that they don't directly state that vote counts aren't accurate. People defending Gore did claim fraud, but I don't remember him saying that, though my memory is fuzzy. Stacey Abrams came the closest that I recall for any major election, but her statement was more that standards were applied too strictly and prevented people from being able to vote or their ballot being returned, which is different from a hidden conspiracy to toss votes such that even ballots that were accepted didn't get counted or that software systematically changed votes. The implications for those two lines of logic are different. One is that even if you get your vote in, you'll be cheated. The other is that you need to do what you can to make sure your vote gets in. I'm happy to be shown I'm wrong though.