Obama has built his public image around his ability to bridge divisions - racial, ideological or generational. And that was his reputation, even at Harvard Law School, where he was the first black president of the 'Law Review.

Donald Trump is a candidate who divided his own party more deeply than any presidential candidate has before.

You have [Donald] Trump and [Ted] Cruz battling it out, and the moderate establishment candidates like Chris Christie or Jeb Bush, Marco Rubio, John Kasich - they have formed a circular firing squad.

White voters were 72 percent of the electorate in 2012, and their share of the population has shrunk a couple points since then. [Donald] Trump has had trouble winning certain segments of the white vote, such as suburban women and college-educated voters.

After months and months at the top of the polls, there is a real possibility that Donald Trump could be the nominee.

As one conservative intellectual said to me - he said if the choice is between [Joseph] Stalin and [Adolf] Hitler, I'd pick Stalin, meaning Ted Cruz because he's more predictable. So there's real civil war inside the Republican Party.

Donald Trump's staffing up a pretty traditional, very conservative Republican government, not a populist outsider government, at least not yet.