U.S. Under Secretary of Defense for Policy Michèle Flournoy arrives for a bilateral meeting with Ma Xiaotian on Dec. 7, 2011 in Beijing, China.
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Here’s who might succeed Chuck Hagel

Just hours after news broke that Chuck Hagel would resign under pressure from the Obama administration, three contenders emerged as likely replacements for the Defense Secretary many critics derided as ineffective.

The Hagel decision—perhaps the biggest shake-up of President Obama’s White House team—comes on the heels of midterm elections largely seen as a rejection of the president’s policies and ahead of his stated plan to request explicit Congressional approval for new military intervention. 

RELATED: Defense Secretary Chuck Hagel forced out

There are three likely candidates to succeed Hagel: Michele Fourney, Ashton Carter, Jack Reed, and Robert Work. They’ll have to make it through a tough approval process led by the Senate Armed Services Committee, and with the president acting without Congressional approval to use airstrikes in Syria and Iraq to fight off ISIS, the confirmation process promises to be particularly contentious and bitter.

Here’s a look at the top candidates.

Ashton Carter is a national security stalwart under Democrats. He joined the Obama administration in 2009, eventually rising to be the Pentagon’s second-in-command from 2011 to 2013. There he managed the Pentagon’s budget, its 2.2 million employees, and rose within the ranks of Obama administration until late 2013, when the 59-year-old resigned after being passed up for the top job Hagel snagged.

A Rhodes Scholar, theoretical physicist, and former Harvard professor with a bachelor’s degree in medieval history, Carter has largely shied away from being a political heavy hitter, the very thing that helped Hagel, a former Republican senator, secure the nomination in 2013.

Michèle Flournoy could be the country’s first female Secretary of Defense. She served as the under secretary of defense for policy until 2012, when she stepped down to “rebalance” her personal life.

Then the most senior woman in Pentagon history, she is a widely respected national security voice, albeit one who has largely kept her head—and her personal views—down. A graduate of Harvard and Oxford University, she started in the Pentagon in the 1990s; she is currently the CEO at the Center for a New American Security (CNAS), a nonpartisan think tank she founded in 2007, that is reportedly relied on by the Obama administration in the development of policy. 

Robert Work is the current No. 2 in command at the Pentagon, the deputy defense secretary, and the only name on this list currently on federal payrolls. He’s worked all over the Pentagon as the undersecretary of the Navy and as a retired Marine colonel. He’s also worked at Fourney’s CNAS—she replaced him at CEO when the Senate confirmed him at the Pentagon earlier this year.

Jack Reed, the Democratic Rhode Island senator in line to become a ranking member of the Senate Armed Committee, was suggested immediately following news of Hagel’s departure, but his spokesman shot the rumor down pretty quickly.

“Senator Reed loves his job and wants to continue serving the people of Rhode Island in the United States Senate,” his spokesman told reporters. “He has made it very clear that he does not wish to be considered for Secretary of Defense or any other cabinet position. He just asked the people of Rhode Island to hire him for another six year term and plans on honoring that commitment.”

Barack Obama, Chuck Hagel, Defense Department and White House

Here's who might succeed Chuck Hagel