The Donald must have needed some publicity. He heard Perry’s reference to Obama and birth certificates and suddenly he is back with support for Perry (at least for his stand, if not for his election). Perry is suffering the same fate as Donald — start out strong then when people actually hear you on issues, the support disappears. Donald is a slow learner when it comes to politics.
For both it was a matter of believing the press clippings, announcing a run, then coming up with a stand on issues. Most presidential winners start with the stand on issues, then run for president.