Who Will Replace Chuck Hagel?

U.S. Secretary of Defense Chuck Hagel resigned on Monday, a move that the New York Times reports President Obama requested last Friday. The decision reportedly came after weeks of meetings between the two, during which it was concluded that Hagel's strengths were not best suited for combatting the ongoing challenges presented by ISIS. Obama officially announced Hagel's resignation on Monday, calling him an "exemplary defense secretary," and stated that Hagel will stay on in his position until a successor is nominated and confirmed. As for who that successor might be, the NYT reported that the Obama administration has already short-listed some early front-runners.

In Monday's announcement, Obama thanked the defense secretary and listed the impressive accomplishments over his career. Obama also emphasized Hagel's contribution to crucial recent missions without commenting on the struggles that have led to his resignation.

Over nearly two years, Chuck has been an exemplary defense secretary, providing a steady hand as we modernize our strategy and budget to meet long-term threats while still responding to immediate challenges like ISIL and Ebola. Thanks to Chuck, our military is on a firmer footing, engaged in these missions, and looking ahead to the future.

Hagel took over the podium, flanked by Obama and Vice President Joe Biden, to give his thanks and closing remarks, so to speak.

It's been the ... greatest privilege of my life to lead, and most important, to serve with the men and women of the Defense Department.... I am immensely proud of what we've accomplished during this time.... I believe we have set not only this department, the Department of Defense, but the nation on a stronger course toward security, stability, and prosperity.

As Hagel wraps up his service as the 24th Secretary of Defense of the United States, let's take a look at who experts are expecting will vie for the coveted position.

Michèle A. Flournoy

Flournoy is one of the first names that come up in discussions to replace Hagel. She served as the Under Secretary of Defense For Policy from 2009 to 2012. Flournoy is currently CEO of Center For a New American Security (CNAS), a nonpartisan think tank that she founded in 2007 and where she served as president until 2009. The organization is believed to have helped the Obama administration develop national security policy.

Robert Work

Work, a retired Marine colonel, is currently the Deputy Secretary of Defense under Hagel. Prior to this position, he served as the CEO of CNAS and was once the Under Secretary of the Navy. As the second in command in the Defense Department, Work has been instrumental in budget and crisis management in recent months. He is also chairman of the Nuclear Deterrent Enterprise Review Group, which assesses the Pentagon's management of its nuclear arsenal.

Ashton B. Carter

Carter was Deputy Secretary of Defense from 2011 to 2013, and before that he was the Under Secretary of Defense for Acquisition, Technology and Logistics from 2009 to 2011. In his five years as the No. 2 and No. 3 positions in the Pentagon, Carter led two major reviews of security budget and strategy, facilitated major DOD logistics programs, and spearheaded international defense partnerships and arms sales.

Senator Jack Reed

Senator Reed's name had also been thrown into the mix, but a spokesperson said on Monday that "he does not wish to be considered for secretary of defense or any other Cabinet." In fact, the Democratic senator from Rhode Island and former officer with the Army’s 82nd Airborne has just "asked the people of Rhode Island to hire him for another six-year term and plans to honor that commitment."

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