Andy, you might want to check out my post about the sterling character Trump has just hired.
Manafort was hired to get Trump's own delegate "ground game" going. In choosing someone Trump was in a tough spot:
* He does not know this stuff well himself as a political novist.
* Many career election people were pressuring others not to work for Trump.
* He needed somebody very competent with a good track record of success.
So maybe its not surprising he hired a guy who had been shunned by the insiders. In Manafort's case of course he was shunned for working for the likes of Victor Yanukovych against the "Orange Revolution". Ironically, he is now working for an orange candidate, what a mercenary the guy is!
Was there a moral failing on Trump's part here like the one I think Cruz had in hiring a slime throwing expert? I don't think so, because Trump is hiring him as a defense in a slimy aspect of politics he is a late comer too, not to bring the campaign to a new low.