The Weekly Standard editor William Kristol tells The Hill that foreign policy will likely be the focus of the 2016 election, and GOP candidates need to prepare.

In particular, he says Wisconsin Gov. Scott Walker, a recent GOP favorite, needs to study up on international affairs to compete at a time when Israel-U.S. relations are being tested, the Iran nuclear deal is pending and ISIS is a growing threat.

“Scott Walker has done in excellent job as governor, but obviously he hasn’t had to deal with these issues much,” Kristol added. “I think foreign defense policy ... will be his next hurdle to overcome."

Take a look at The Hill's video for Kristol's take on other possible contenders vying for the GOP's presidential nomination in 2016.