a.) Trump's use of wiggle words to give himself leeway (for those who can/will read nuance)-- alluding to but not quite saying stuff (e.g., "I have real doubts") and making claims that sound reasonable enough but are probably wrong (e.g., Hillary was behind the birther controversy). In this, he parallels (Bill and Hillary) Clinton's lawyerly lies/answers/approach. Trump is famous for his bombast but in one sense-- and in certain contexts-- I'm convinced that he's choosing his words as carefully as Clinton.
b.) The author says the birther controversy came from Clinton supporters, but not the campaign. I hadn't thought about it this earlier, assuming the whole thing was a GOP invention. But it makes more sense that it would have popped up during the Democratic primary, alongside the oodles of racism I saw among Democrats when I was on the campaign trail in 2008. Ironic.
c.) I think Trump's original goal was to use the GOP primary as business self-promotion. Then he stumbled into winning when the GOP fielded so many (mediocre) candidates. He's annoying but good at self-promotion and intently focused on it. This episode seems to be more evidence about that means/end.