YOU”RE FIRED, or so says Eric Trump about Paul Manafort. He highly suggests in this video that Manafort was fired because he was distracting Trump with his Ukrainian problems and issues, when the focus needed to be on what Trump was saying and what the problems were with Hillary Clinton. The distraction was just too much for the Trump campaign to deal with, so in the end Paul Manafort was pushed out the door and sent packing.
https://youtu.be/KpHowS22gMQ