Alex Wong/Getty Images

No one ever suggested Donald Trump is a patient, meditative, reflective decision-maker, but more and more his impulsive behavior and unwillingness or incapability to focus is raising concerns about how he would run the White House.

"I think he's definitely got attention deficit disorder. That doesn't mean he isn't really smart — it just means he's not at his best when he's asked to dwell on a topic," Trump biographer Michael D'Antonio told Politico.

Trump has offered conflicting thoughts on his own ability to focus, claiming both "I have an attention span that's as long as it has to be" to Time last year, and outright admitting "my attention span is short" in his 1990 book Surviving at the Top.

This much is clear though: Trump would certainly be a contrast to the current president, "a reader by disposition and a lawyer by training who stays up late plowing through 'an insane amount of paper,'" Politico writes. George W. Bush also "read volumes of material every night." But Trump has said he doesn't like long reports: "Send me, like, three pages," he told Washington Post reporters of his briefing preferences. And on reading in general, he says he "doesn't have much time."

Jack O'Donnell, who served as one of Trump's Atlantic City casino executives, has seen how this works out, at least in the business world. O'Donnell recalled that when he worked for successful casino magnate Steve Wynn, the two would have eight- or nine-hour meetings.

That wasn't how Trump did things. "He would talk for a few minutes and then change the subject," O'Donnell said. "I don't think he has the capacity to listen."