A constitution should have peace and prosperity for the country as one of its goals. This means that force against the people should be the monopoly of an institution that is governed by laws in order to uphold at least a minimum amount of order in pursuit of the other goals. That legitimizes police.
Now we get to the matter of how a certain constitutional order is allowed to defend itself against domestic threats within its own legal framework. The US constitution relies a lot on balance of power and does not regulate much else in case that this fails. I do not know of any constitutional right for a congressman to lead violent actions against other parts of the government. And that leads to the situation where the most effective actions to restore order are more detrimental to that order in the short term.
And the Democratic party is refusing to go there. Think of that what you will, but that's why their actions amd responses are so tame.