WASHINGTON — Secretary of Defense Chuck Hagel resigned Monday, in a move that had been rumored for weeks.

President Barack Obama made the official announcement from the Rose Garden at 9 a.m. MST Monday, and officials said the decision had been made as of last Friday.

Obama is not expected to announce a successor, a White House official said. That official said that the short list to replace Hagel includes former Under Secretary of Defense for Policy Michèle Flournoy, former Deputy Secretary of Defense Ash Carter and Rhode Island Sen. Jack Reed, a former paratrooper.

Hagel, a former Republican senator from Nebraska, has held the post as Secretary of Defense since February 2013.

The New York Times reported that officials from Obama’s office said Hagel’s nudge into resignation was a recognition by the President that the threat from the Islamic State would require a different kind of skills than those that Hagel was brought on to employ.

Hagel wasn’t fired, a White House official told the Times, but rather mutually agreed with the president that it was time for him to go.

“The next couple of years will demand a different kind of focus,” an administration official told the Times.

A critic of the Iraq war, Hagel was brought on to oversee withdrawal from Afghanistan and a smaller Pentagon budget than ever before.

Hagel’s aides have said the Defense Secretary, the last remaining Republican on Obama’s national security team, had planned to serve out his full four years in office.

Hagel’s tenure was rocky before it even began.

During his confirmation hearings, Hagel drew sharp criticism from pro-Israel Republicans concerned with his opposition to aggressive sanctions against Iran and for his criticism of the Defense Department as “bloated.” His confirmation was filibustered before he ultimately won approval.

And his two years at the Pentagon have been marred by gaffes that occasionally undercut the President and an inability to sell the administration’s national security policy.

He at one point called ISIS an “imminent threat to every interest we have,” contradicting the President’s comments just months before that the group was simply “junior varsity.”

The administration has taken persistent criticism over the past few months as a series of national security crises roiled the nation, and the President’s response was seen by many as flat-footed and inconsistent.

Hagel’s departure has been rumored to be coming for weeks, and as recently as last week he dodged questions about his continued tenure at the Pentagon.

“First of all, I serve at the pleasure of the President,” Hagel told PBS, asked whether he’d continue in the position. “I’m immensely grateful for the opportunity I’ve had the last two years to work every day for the country and for the men and women who serve this country. I don’t get up in the morning and worry about my job. It’s not unusual by the way, to change teams at different times.”

Pressed on whether he felt he still had Obama’s confidence, Hagel said, “Well, I don’t think I would be here if I didn’t. But you’d have to ask him that. I mean I see him all the time.”

CNN contributed to this report.

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