Say what you will about liberals/leftists, when 2016 happened, Hilary Clinton and the Dems didn't blabber on about how the election was stolen and how the other side was trying to hold her down. Hilary and the Dems didn't use stochastic terrorist rhetoric to galvanize their base into attempting to stop the certification of the election.
If Trump wins, Kamala and the Dems will be upset but they will at least acknowledge the loss and Biden will commit to peacefully handing power over to Trump. After 2020, there is no guarantee that Trump or his followers will respect the results of the election in the even of a Kamala victory. Trump has no respect for the democratic process, that is why he's unfit to be President.