Defense Secretary Chuck Hagel resigned Monday, in the first cabinet-level departure after the Democratic losses in the Senate in the midterm elections.
Hagel's successor will be named "in short order," a senior administration official told BuzzFeed News. At a news conference on Monday morning, Hagel said he will remain in his post "and work just as hard" until his replacement is confirmed by the Senate.
At the news conference, Obama praised Hagel, 68, as "a young army sergeant from Vietnam who rose to serve as America's 24th secretary of defense."
Referencing the troops, Obama said Hagel "stood where they stood. He's been in the dirt and he's been in the mud." Obama, calling Hagel a "friend," added that "this decision does not come easily to him."
"When it's mattered most, behind closed doors, in the Oval Office, you've always given it to me straight," Obama said, seemingly referencing recent reports that Hagel wasn't outspoken in open meetings with the president and his close advisors.
The New York Times reported that Hagel resigned "under pressure," saying the decision was "a recognition that the threat from the militant group Islamic State will require different skills from those that Mr. Hagel, who often struggled to articulate a clear viewpoint and was widely viewed as a passive defense secretary, was brought in to employ."
In October, Hagel, a Republican, began speaking with the president about departing the administration after the midterm elections. Those conversations were ongoing for several weeks, the senior administration official confirmed to BuzzFeed News.
A source familiar with the Pentagon told BuzzFeed News that Obama met Hagel at the White House on Tuesday to discuss the matter. On Thursday, the source said, the White House Chief of Staff Denis McDonough went to Hagel's office at the Pentagon, where the two met alone.
Sen. John McCain, a Republican from Arizona, said he knew "that Chuck was frustrated with aspects of the Administration's national security policy and decision-making process." The comment echoed criticisms made by former Defense Secretary Robert Gates after he left the Obama administration in 2011.
"Chuck and I have worked well together, and we have often seen eye to eye on our biggest national security challenges — ISIS, the conflict in Syria, the war in Afghanistan, a rising China, and, most of all, sequestration," McCain added.
House Speaker John Boehner said, "This personnel change must be part of a larger re-thinking of our strategy to confront the threats we face abroad, especially the threat posed by the rise of ISIL."
Hagel was sworn in as defense secretary in February 2013. Before that he was a U.S. senator from Nebraska. He has helped managed the troop drawdown in Afghanistan and dealt with a significantly reduced Pentagon budget after sequestration, Obama said.
Hagel also helped address the "scourge of sexual assault from the ranks," Obama said.
Michèle Flournoy, a former undersecretary of defense for policy, and Democratic Sen Jack Reed, a former Army officer from Rhode Island, have been mentioned by Pentagon officials and Capitol Hill sources as possible replacements.