Sure, your reasoning makes sense if you also do not care about the harm he has done to the nation as a whole. See, if Democrats had their heads stuck so far up their asses that they only cared about harming the Republican party electorally, they would consider Trump an asset. But, because they share a country with Republicans, and know that Trump will harm everyone—even more than he already has—they will push to have him punished in every way possible. Criminals who attack democracy, get hundreds of thousands of people killed, and traumatize thousands of children and their parents must be punished and prevented from ever being able to do anything like that again. It's a matter of principle and a matter of self-preservation. For people who don't have their heads stuck up their asses