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)

Twin baby panthers Remaong and Ferra cling to their basket while being presented to the media at Tierpark Berlin zoo on July 13, 2012 in Berlin, Germany. The two panthers were born in captivity on April 26. (Photo by Sean Gallup)

Former Soviet President Mikhail Gorbachev and his daughter Irina Virganskaya attend the Free Your Mind Award Presentation at the Cinema For Peace charity dinner at the China Club on November 8, 2009 in Berlin, Germany. (Photo by Sean Gallup/Getty Images). BERLIN – NOVEMBER 08 2009

Finia, a visiting student from Hanover, cools off under a water sprinkler in front of the Chancellery on June 10, 2010 in Berlin, Germany. (Photo by Sean Gallup/Getty Images)

A baby hippopotamus lies next to its mother on the first day it was presented to the public at the Zoo Berlin zoo on November 1, 2011 in Berlin, Germany. The baby hippo was born at the zoo on October 23. (Photo by Sean Gallup/Getty Images)

The giant mural titled “Under the Hand” by Maclaim Crew is visible on a building facade in Kreuzberg district on June 26, 2014 in Berlin, Germany. Berlin, with its long tradition of counter-culture, has become a mecca for street art of all dimensions and messages. (Photo by Sean Gallup/Getty Images)

Summit, an Australian shepherd, makes a leaping catch of a frisbee at the pet trade fair (Heimtiermesse) at Velodrom on November 2, 2012 in Berlin, Germany. Exhibitors are showing the latest trends in collars, snacks and other accessories for cats, dogs and other household pets. (Photo by Sean Gallup)

Participants dressed as Santa Claus gather shortly before the 4th annual Michendorf Santa Run (Michendorfer Nikolauslauf) on December 9, 2012 in Michendorf, Germany. Over 800 people took part in this year's races that included children's and adults' races. (Photo by Sean Gallup)