The problem with this tweet is that it ignores the context in the 2016 election that would lead Pelosi to issue such a warning.
Namely, for months prior to the election, Trump claimed that the only way he would lose is if the election was rigged. And at rally after rally, he said it would be rigged. Most of us understood this to just be a way to make it appear he was cheated out of a win. He would never accept the fact that he could possibly truly lose at anything, after all:
https://www.politico.com/story/2016/08/donald-trump-rigged-election-226588
Then, during the last debate of 2016, he refused to say he would concede the election if he lost, thereby threatening the peaceful transfer of power:
https://www.usatoday.com/story/news...ald-trump-election-results-reaction/92445068/
"Donald Trump has, in recent days, blasted the presidential campaign as "rigged," and at Wednesday's debate in Las Vegas, he was asked whether he would accept the election results, no matter the outcome.
He refused to make that commitment, saying he would "look at it at the time." When pressed again by moderator Chris Wallace, the GOP nominee said: “I will tell you at the time. I will keep you in suspense.”
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He later revised that by saying he would accept the results, if he won! Lol....
So, given this context, how can anyone blame Pelosi for feeling this way? After all, he has already overseen an increasing trend toward authoritarianism:
1. He has eliminated an independent DOJ, by appointing an AG that is no longer the people's AG, but simply another one of his legal defenders.
2. He is attempting to eliminate the Constitutional right of the Legislative branch to excercise oversight over the Executive branch, by simply ignoring every and all requests and supeanas pertaining to documents and testimony. Including suing Deutche Bank to keep his finances unseen. That may be justified, but it's more likely there are things he does not want the public to see, just as he continues to block access to his tax returns. This ignoring of the House also threatens our system that recognizes that all three branches of the federal government are equals.
Given these already obvious trends toward increasing the power of an imperial presidency, bolstered by an AG who believes in unlimited power for the Executive branch( and it's appropriate that Kamala Harris had asked the IG to find out if Trump has directed the AG to go after Trump's enemies), of course we should not expect a peaceful transition if Trump lost a close election in 2020. Even his supporters should be willing to admit that much.
Does anyone really believe he would pull an Al Gore and concede a close election, to preserve our tradition of peaceful transition? At the least, such an outcome goes against everything we know about Donald Trump. It would be completely out of character.