Trump's Challenge In Uniting The GOP

As the apparent Republican presidential nominee, Donald Trump faces a big hurdle trying to bring the party together to support his candidacy. And the challenge includes the lack of support he'll get from top figures in the party.

Former presidents George H.W. and George W. Bush are going to stay on the sidelines of the race and 2012 GOP nominee Mitt Romney has campaigned against Trump. Here & Now's Jeremy Hobson talks with Julian Zelizer, a political historian and professor of history and public affairs at Princeton's Woodrow Wilson School.