Two things.
First, Trump broke the law in buying politicians. That is well beyond “optics”. His ambition exceeded his morality.
Second, do you not believe Cruz learned his lesson on the immigration issue?
There’s always been a mix of politics and business, and some of that does turn into illegalities. If Trump had illegal dealings with any politician, I’m sure it would have come out by now. Merely donating to a politicians campaign is not illegal, but if you can prove that the politician was actually receiving bribes, that’s illegal. So, if you think that Trump’s deals were illegal, you are more than welcome to invest a lot of time examining all of his dealings. I would think that Cruz, Rubio, Bush, Clinton, etc., have probably had their Opposition Research crews working on this very subject for many months. We’ll have to wait and see, but by all means, start your own investigation if you want.