http://www.nytimes.com/2016/07/20/magazine/how-donald-trump-picked-his-running-mate.html?_r=0
But according to the Kasich adviser (who spoke only under the condition that he not be named), Donald Jr. wanted to make him an offer nonetheless: Did he have any interest in being the most powerful vice president in history?
When Kasich’s adviser asked how this would be the case, Donald Jr. explained that his father’s vice president would be in charge of domestic and foreign policy.
Then what, the adviser asked, would Trump be in charge of?
“Making America great again” was the casual reply.
[Manafort] “He needs an experienced person to do the part of the job he doesn’t want to do. He seems himself more as the chairman of the board, than even the CEO, let alone the COO.”
Trump wants to win the presidency and not actually be president. A worse George W. Bush who knows and understands government/policy and who's even less interested in the day to day.