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The problem with the "polls" is that some people may actually believe them and when their candidate looses spectacularly they naturally get convinced that it had to be a fraud and then it happens what it happened.
My question is, if Trump is allowed to run (a big if) and if he looses again, will he call on an assault on the Capitol again and praise the people performing such an act?
I don't think Trump would dare to call for their followers to explicitly assault anything or anyone in the case he lose the presidency of his country. The fact he is bad mouthing people now and believe he cannot be touchedz it is because he takes advantage of his state as leading candidate for the Republican party. If he loses he will likely just stay home and ask his lawyers to somehow use his private citizen status to get him out of trouble.
The kind of assault that the Trump people - average American citizens around the country - are doing right now is an assault on the evil in government. The people are waking up to the evil of the Dems and RINO's, especially including Biden and his team, and will be casting them out of government come some of the next elections, including the 2024 Presidential election.

As long as Biden is cast out the government, as you say, through democratic means, then it should not be a problem, the trouble comes when the democratic system itself is the one under siege because many people did not like the result. And let me remind you: one of the most important parts of democracy is the losing part to accept defeat and move on.
I am aware there are millions of people in the United States who disapprove the administration of Biden, that is fine and they have the right to express their disapproval, under their first amendment. But the constitution cannot be used as a tool to destroy the same laws there are written in it. And the first amendment is not supposed to protect difamation, for example.