“He is brilliant and driven, a policy wonk equally adept at mastering the bureaucracy,” says a former White House official. “He’s also arrogant, and doesn’t suffer fools gladly.”

That could be a warning sign in an administration that has already burned through three defense secretaries who resented White House micromanagement of their affairs. In Carter, Obama would be choosing a strong-willed independent thinker who believed the U.S. should have left a robust residual troop force in Iraq and believes the military has been asked to swallow dangerously large budget cuts. Carter’s record on nuclear non-proliferation also suggests he could take a harder line on Iran policy than Obama favors.

A bona fide scholar whose pursuits have ranged from the monks of 12th century Flanders to quark theory to nuclear terrorism, Carter has surely earned his self-confidence. But as he prepares for the top military job amid uncertainty in Iraq and Syria, the question is whether a wonk is what America needs in wartime.

“Ash Carter is widely recognized as one of the country’s sharpest policy minds, which leads some to question whether or not he can actually run a war,” says Julianne Smith, a former deputy national security advisor to vice president Joe Biden now at the Center for a New American Security.