Senator Barack Obama (D-IL) (R) stands in front of Senator Hillary Clinton (D-NY) as they arrive for U.S. President George W. Bush's annual State of the Union speech to a joint session of Congress at the U.S. Capitol in Washington in this January 23, 2007 file photo. Hillary Clinton announced her second run for the presidency on April 12, 2015 starting her campaign as the Democrats' best hope of fending off a crowded field of lesser-known Republican rivals and retaining the White House. (Photo by Larry Downing/Reuters)

Activists protest the Shell Oil Company's drilling rig Polar Pioneer which is parked at Terminal 5 at the Port of Seattle, Washington May 16, 2015. Hundreds of activists in kayaks and small boats fanned out on a Seattle bay on Saturday to protest plans by Royal Dutch Shell to resume oil exploration in the Arctic and keep two of its drilling rigs stored in the city's port. (Photo by Jason Redmond/Reuters)

Gunfire was brought to the steps of President Truman's Washington home, Blair House, as two assassins tried to kill the chief executive, November 1, 1950. One of the gunmen, Oscar Collazzo of New York, lay wounded at the bottom of Blair House's front steps after the president's police guard had finished their work, at the cost of one guards' life, Dec. 9, 1950. The second gunman was killed. (Photo by Harvey Georges/AP Photo)

Yippie leader Jerry Rubin, barred on December 4, from House Un-American Activities subcommittee hearing, aims a toy gun in “self defense” outside the Washington hearing room on December 5, 1969. Rubin showed up in his Santa Clause suit because he believed it was typical of the committee which, he said, “is a total circus”. (Photo by Bob Daugherty/AP Photo)

Volunteers receive a professional massage from qualified therapists as they break a world record for the largest ever simultaneous massage during Massage en Masse at Lavandula Lavender Farm on March 30, 2010 in Daylesford, Australia. Two hundred and sixty three massage therapists each massaged a volunteer, breaking the former world record of 167, set in 2009 in Washington DC. (Photo by Scott Barbour/Getty Images)

David Sharp, an engineer with Lockheed Martin, displays the “Samurai Flyer”, an aviation design inspired by the maple seed, during the Association for Unmanned Vehicle Systems International Conference August 16, 2011 in Washington, DC. Lockheed Martin unveiled the new design and demonstrated vertical takeoff and landing, stable hover, and on-board video streaming of the aircraft during their demonstration. (Photo by Win McNamee/Getty Images)

A competitor looses control of his pancake while racing during the Shrove Tuesday, or Mardi Gras, tradition at the National Cathedral February 21, 2012 in Washington, DC. (Photo by Chip Somodevilla/Getty Images)

Yanelis Blanco, 24, center, dances with a group of friends at Santa Maria beach, about 15 miles from Havana. It is the closest beach to Havana. Others, from left to right are Jackson Miranda, 21, Dayan Suarez, 24, and Melisa Oliva, 15. The men in the group have a rap group together. The government is demolishing buildings all over the coast of East Havana and recovering and restoring beach dunes. (Photo by Sarah L. Voisin/The Washington Post)