They're all scum and criminals. Some more than others. I won't defend garbage politicians who represent my interests, the same way I won't defend garbage politicians that don't.
If they're garbage and criminals, they should be prosecuted regardless of what they stand for or vote for. Nobody is above the law.
I don't know what people don't get about all people being equal, but that's what it is. We are all citizens, we are all responsible for our own actions, and if we do the illegal, then we should face the consequences of that action regardless of who we are, or what we do, or how much money/influence/whatever, we may possess.
I know it doesn't work that way. Some people get away with shit constantly because they're rich/influential/whatever, but that reality doesn't impact my perspective on the matter. They should be prosecuted, whether they are or not is another issue entirely. Given the choice to have people investigated or not for crimes, I say go for it. If the people convicted are those that I may have voted for or supported in the past, then I'm glad they've been convicted and removed. They probably didn't deserve my support, but I can only operate on information I have, not information of what might be true...
It's also worth noting that people with undisclosed skeletons in their closet are blackmailable. So even if they represented your interests in the past that all ends once someone puts them on a leash. This is why even if you make no moral judgements there are pragmatic reasons to not have such people in office.