President Barack Obama visits a classroom of pre-schoolers and teachers following remarks at Adas Israel Congregation in Washington, D.C., May 22, 2015. (Official White House Photo by Pete Souza)

President Barack Obama holds a meeting in the Oval Office to discuss the Senate cloture vote on trade promotion authority before its passage, May 21, 2015. (Official White House Photo by Pete Souza)

President Barack Obama shares a moment with newly commissioned ensigns during commencement at the U.S. Coast Guard Academy in New London, Conn., May 20, 2015. (Official White House Photos by Pete Souza)

President Barack Obama and Vice President Joe Biden greet the families of slain Officers Ramos and Liu after the signing of the Rafael Ramos and Wenjian Liu National Blue Alert Act of 2015 in the Oval Office, May 19, 2015. The bill is to establish an alert system for police threats in the wake of the ambush killings of the two NYPD officers in Brooklyn, N.Y. (Official White House Photo by Pete Souza)

President Barack Obama talks with students and law enforcement officials following a sit-down discussion at the Salvation Army Ray and Joan Kroc Corps Community Center in Camden, N.J., May 18, 2015. (Official White House Photo by Pete Souza)

Gen. Martin E. Dempsey, 18th chairman of the Joint Chiefs of Staff, and ​Lt. Gen. Robert L. Caslen, Jr., the 59th Superintendent of the U.S. Military Academy at West Point, return salutes to the graduating class of 2015 at the U.S. Military Academy at West Point, N.Y., May 23, 2015. DOD photo by D. Myles Cullen/Released)

Defense Secretary Ash Carter welcomes families of the Tragedy Assistance Program for Survivors, known as TAPS, to the Pentagon, May 22, 2015. The program offers support for military families who have lost a family member serving in the military.

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U.S. 5TH FLEET AREA OF OPERATIONS (May 20, 2015) An MH-60S Sea Hawk helicopter assigned to the Sea Knights of Helicopter Sea Combat Squadron (HSC) 22 picks up supplies from the Military Sealift Command Fast Combat Support Ship USNS Arctic (T-AOE 8) during an underway replenishment with the aircraft carrier USS Theodore Roosevelt (CVN 71). Theodore Roosevelt is deployed in the U.S. 5th Fleet area of operations supporting Operation Inherent Resolve, strike operations in Iraq and Syria as directed, maritime security operations and theater security cooperation efforts in the region. (U.S. Navy photo by Mass Communication Specialist 3rd Class Josh Petrosino/Released)

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CARIBBEAN SEA (May 18, 2015) Dr. Judith Brill, a physician volunteering with the non-governmental organization Operation Smile, comforts a Nicaraguan patient in the post-operating room aboard the Military Sealift Command hospital ship USNS Comfort (T-AH 20) during Continuing Promise 2015. Operation Smile volunteer medical professionals will provide free cleft lip and cleft palate surgery to hundreds of patients during Continuing Promise. Continuing Promise is a U.S. Southern Command-sponsored and U.S. Naval Forces Southern Command/U.S. 4th Fleet-conducted deployment to conduct civil-military operations including humanitarian-civil assistance, subject matter expert exchanges, medical, dental, veterinary and engineering support and disaster response to partner nations and to show U.S. support and commitment to Central and South America and the Caribbean. (U.S. Army photo by Spc. Lance Hartung/Released)