Obama nominates Pentagon veteran Ashton Carter as his 4th Defense Secretary – has never served in the military

President Barack Obama shares a laugh with Ashton Carter, his nominee for defense secretary, Friday during the announcement in the Roosevelt Room of the White House. Associated Press

WASHINGTON—President Barack Obama on Friday nominated Ashton Carter to be his fourth defense secretary, elevating a Pentagon veteran to lead the nation’s military as it faces growing conflict in the Middle East.

Should he be confirmed by the Senate, Mr. Carter would take over a Defense Department constrained by slimmer budgets that could make it harder to combat global threats, from Islamic State fighters trying to carve out an extremist enclave in the Middle East to Russian forces testing the fortitude of the North Atlantic Treaty Organization.

Mr. Carter would replace Defense Secretary Chuck Hagel, the former Republican senator from Nebraska who was forced from the job last week by a White House seeking a jolt of energy as the president winds up his second term.

“Ash is rightly regarded as one of our foremost national security leaders,” Mr. Obama said. Calling Mr. Carter an innovator and a reformer, the president said his nominee would hit the ground running on day one. “He knows the Department of Defense inside and out,” Mr. Obama said.

Mr. Hagel didn’t attend Friday’s announcement. A Defense official said the outgoing secretary believes this is a day to celebrate Mr. Carter and his family, and Mr. Hagel didn’t want to distract from that focus.

Mr. Carter said he accepted the nomination because of his regard for Mr. Obama’s leadership, because of the seriousness of the challenges the U.S. faces and because of the deep respect and he has for the men and women in uniform.

Ashton Carter’s been a theoretical physicist, a medieval scholar and a nuclear weapons expert. He’s now Barack Obama’s pick for Secretary of Defense. He can run rings around most people in the IQ department but can he run a war?

”If confirmed in this job, I pledge to you my most candid strategic advice,” Mr. Carter told the president. “And I pledge also that you will receive equally candid military advice.”

Mr. Carter is known for his policy prowess, but many question what impact he will be able to have with a White House criticized by his predecessors for micromanagement. The White House denies those accusations.

But his experience at the Pentagon, where Mr. Carter held the job as deputy defense secretary until last December, is expected to pave the way for a relatively smooth transition.

Key senators have suggested that, barring any unforeseen surprises, Mr. Carter is likely to have a smooth confirmation process. Still, his confirmation hearing is expected to become a proxy battleground for Republican critiques of the president’s foreign policy.

The 60-year-old physicist, who never served in the military, would come to the job with extensive Pentagon experience. President Bill Clinton tapped him in 1993 to serve as an assistant defense secretary overseeing nuclear-weapons policy and military relations with the former Soviet states—a job he held for three years.

In 2009, Mr. Carter took the job as the Pentagon’s undersecretary of defense overseeing the beleaguered system for developing and building military gear, including America’s costly new F-35 jet fighter. Two years later, he was elevated to deputy defense secretary.

Michael O’Hanlon, co-director with the Brookings Institution’s Center for 21st Century Security and Intelligence, said Mr. Carter has to enter the Pentagon with the ability to push new policies, especially in the Middle East where U.S. Central Command is sending thousands of troops into a growing conflict with Islamic State fighters.

The new Middle East fight is proving to be one of the biggest challenges Mr. Obama faces as he prepares to leave office, and his strategy has generated criticism in Washington, where many Republicans are pushing for a more aggressive military response.

“The fact that he’s an administration alum doesn’t preclude fresh thinking on his part, but it does raise the concern that the White House will have hired him thinking he’s more a loyalist than a creative/disruptive force,” Mr. O’Hanlon said.

Mr. Carter’s constraints may not only come from the White House.

“If people were looking for a dramatic departure from current defense policy, then that’s probably not what we will see from Carter,” said Todd Harrison, a defense expert at the Center for Strategic and Budgetary Assessments. “But how much change would even be possible in the remaining two years of the administration anyway?”

Mr. Harrison said the defense secretary always made his biggest mark in the annual budget, something Mr. Carter wouldn’t be able to seriously affect until 2017—just as the administration is ending.

Even so, Mr. Carter could become an unexpected new voice in the administration, especially on issues he knows well: nuclear weapons, North Korea and Iran.

In the past, Mr. Carter has demonstrated a willingness to stake out contentious positions. In 2006, to prevent the country from developing a nuclear weapon capable of hitting the U.S., he and former Defense Secretary William J. Perry called on the U.S. to use cruise missiles to destroy a North Korean long-range missile it continues to test and develop.

He has also demonstrated that he has thick skin—and that he understands the take-no-prisoners environment in Washington.

“Public service at senior levels in Washington is a little bit like being a Christian in the Coliseum,” Mr. Carter wrote in a short autobiography he penned in 2007 while teaching at Harvard University. “You never know when they are going to release the lions and have you torn apart for the amusement of the onlookers.”