We aren't talking about an insurrection against constitutional order. The hypothetical is that Trump loses the election, he cites some bogus case of fraud like he has spent the last several months building, he refuses to concede just like he said he wouldn't concede if their was fraud, large protests pop up in response to these moves as would obviously happen, Trump declares them riots just like he has been calling the largely peaceful protests of the last several months riots, and he orders in the troops to squash dissent just like he said he would when he refused to agree to a peaceful transfer of power. All of this is based off Trumps own words and prior behavior. It isn't the most likely scenario, but it can't be completely dismissed. It is a situation that the other branches of government and the military need to seriously consider.