Arnie Seipel

Today was a big day in Iowa. And the reason had nothing to do with politics. The University of Iowa Hawkeyes drove into Ames to take on the Iowa State Cyclones in the annual CyHawk football game.

This has been the Summer of Trump on the campaign trail. Donald Trump has flown high in the polls, with seemingly nothing emerging to slow his rise.

But as heading into September, here are three hurdles the reigning Republican front-runner might have to contend with that run counter to his success so far:

Erick Erickson is the man who turned Donald Trump away.

The editor-in-chief of RedState.com stood before the crowd of conservative activists at the RedState Gathering in Atlanta on Saturday and seemed to bask in his rejection of the man who has been leading the polls in the Republican presidential race for weeks.

President Obama wants to close the prison at the U.S. Navy base at Guantanamo Bay before leaving office. But his departing defense secretary, Chuck Hagel, told NPR News the job is "going to be very difficult" to complete in that time.

Hagel made that remark in an exit interview Friday, one of only a handful he granted as he prepared to vacate his expansive office at the Pentagon. The interview will air Monday on Morning Edition.

This story is part of the New Boom series on millennials in America.

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