WASHINGTON — Defense Secretary Chuck Hagel is stepping down from his post after 21 months in office amid tension with the White House over strategy and the rise of new security challenges to the country.
President Barack Obama called Hagel a steady hand at the Defense Department during a time of transition, with the United States winding down its presence in Afghanistan, confronting new threats from the terrorist Islamic State group, and dealing with a strained defense budget.
"Over nearly two years, Chuck has been an exemplary defense secretary as we modernized our budget and our strategy to face long-term threats," Obama said at a White House ceremony Monday morning. Hagel will remain defense secretary until a successor has been confirmed by the Senate, he said.
Obama didn't name a replacement. Potential nominees include former Deputy Defense Secretary Ashton Carter and Michele Flournoy, a former undersecretary of defense. Sen. Jack Reed, a Rhode Island Democrat and West Point graduate, also has been mentioned as a possible candidate, though his spokesman said Monday he doesn't want to be considered.
Hagel's time at the Pentagon has been focused on the reshaping of the U.S. armed forces in the face of budget cuts. He's been in the spotlight recently because the rise of Islamic State in Iraq and Syria has forced the U.S. military to re- engage in the Middle East.
Hagel, 68, a former Nebraska senator and a decorated Vietnam war veteran, resigned by mutual agreement after a series of White House meetings in the past few weeks, said a defense official, who spoke on condition of anonymity to talk about personnel matters.
The departure of the only Republican in Obama's cabinet follows months of increasingly strained relations between Hagel and Obama's national security team.
"On paper, Hagel looked perfect for the job — a war hero, a former Senator, a successful entrepreneur," said Loren Thompson of the Lexington Institute in Arlington, Virginia. "But his confirmation hearings did not go well, and his temperament proved ill-suited to such a politically sensitive job."
Defense officials said Hagel had been marginalized in the administration. One defense official said Hagel had stopped speaking up at White House meetings because Obama's aides with less experience in military affairs often ignored what he said.
Instead, he took to phoning the president after returning to his Pentagon office to shoot down what he considered bad ideas.
Senior members of Obama's national security team, often considered insular by Defense and State Department officials, also clashed with Hagel over U.S. strategy in Syria and in countering the Islamic State. His public appearances, where he at times appeared out of step with the White House, also raised concerns, according to one official, who spoke on condition of anonymity to talk about internal discussions.
Hagel chafed at the centralized White House control of public statements and messaging, which aides said made it more difficult for him to articulate his thoughts, officials close to the defense secretary said.
"I know that Chuck was frustrated with aspects of the administration's national security policy and decision-making process," Arizona Republican Sen. John McCain said in a statement.
"His predecessors have spoken about the excessive micro- management they faced from the White House and how that made it more difficult to do their jobs successfully. Chuck's situation was no different," McCain, who will take over as chairman of the Armed Services Committee when the new Republican majority is seated in January, said.
Senate Republican leader Mitch McConnell of Kentucky said Hagel's departure "comes at a moment of great peril for our country."
Hagel's replacement, whose nomination will be subject to confirmation by the Senate, must be equipped to develop a strategy for modernizing U.S. armed forces while dealing with challenges to the U.S. including those from Russia and China, McConnell said in a statement.
Hagel, a decorated Vietnam war veteran, was picked by Obama to replace Leon Panetta in 2013 as the Pentagon's leader. The choice was criticized by Hagel's fellow Republicans over his past opposition to unilateral sanctions against Iran, his comments about the influence of what he once called "the Jewish lobby," and his opposition to the 2007 U.S. troop surge in Iraq. Hagel faced an onslaught of criticisms from Republicans at his confirmation hearing.
"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," Hagel said Monday at the White House. "If I didn't believe that, I would not have done this job."
A lame-duck administration, continuing pressure on the defense budget, a Republican-controlled Congress and a Senate Armed Services Committee headed by Obama critic McCain will be some of the obstacles facing Hagel's successor.
In addition, Pentagon officials said, the next defense secretary will be caught as Hagel has been between a White House bent on keeping U.S. military engagement in Syria, Iraq and Afghanistan to a minimum and mounting evidence that greater involvement in the war against Islamic State and a much slower withdrawal from Afghanistan are needed to prevent Islamic extremists from seizing control of more of both countries and threatening additional ones.
So far, said the officials, who spoke on the condition of anonymity to talk about internal debates, Obama and his inner circle have responded to recommendations for greater U.S. involvement in Iraq and Afghanistan from Hagel and the Joint Chiefs of Staff with what they called half measures, including an authorization for American forces in Afghanistan to protect themselves and limited additional trainers and advisers for the Iraqi military and Sunni tribes.
The next defense secretary's job will also be complicated by the prospect of interacting with members of Congress who are competing to win the Republican presidential nomination in 2016.
One of the potential presidential candidates, Kentucky Republican Sen. Rand Paul, is urging his colleagues to adopt a formal declaration of war against Islamic State, albeit one designed to limit the president's authority to use ground combat forces in Iraq and Syria. Republican Sen. Ted Cruz of Texas, another member of the chamber considering a run, serves on Armed Services and will have the chance to question the nominee during confirmation hearings.