Buildings in Nogales, Mexico (R) are separated by a border fence from Nogales, Arizona, United Sates, October 9, 2016. Building a wall along the U.S.- Mexico border has been a contentious subject in this year's U.S. presidential election. In parts of California and Arizona, a wall already exists. It runs across rocky deserts, flowing sand dunes and miles of agricultural land. (Photo by Mike Blake/Reuters)

A vehicle leaves light trails in a long exposure photograph as it drives beneath the 500-metre Aperture Spherical Radio Telescope in Pingtang county, China. Construction on the device began in 2011 and is nearing completion. (Photo by Liu Xu/AP Photo)

A kite flying contest is held in Nantong, east China's Jiangsu featuring various kites of different shapes on December 20, 2017. (Photo by SIPA Asia/Pacific Press/Barcroft Images)

In this November 3, 2015 file photo, Afghan Taliban fighters listen to Mullah Mohammed Rasool, the newly-elected leader of a breakaway faction of the Taliban, in Farah province, Afghanistan. Despite US President Donald Trump’s pronouncement that there would be no talks with the Taliban following a series of deadly attacks in Kabul, officials say talks continue, but neither side trusts the other and neither believes the other negotiates independently. (Photo by AP Photo/Stringer)

A demonstrator is carried during a rally in support of a identity check draft law and against delinquency, in Santiago, Chile April 30, 2016. (Photo by Carlos Vera/Reuters)

Residents wade through flood waters from Tropical Storm Harvey in Beaumont Place, Houston, Texas on August 28, 2017. Houston was still largely paralyzed Monday, and there was no relief in sight from the storm that spun into Texas as a Category 4 hurricane, then parked itself over the Gulf Coast. (Photo by Jonathan Bachman/Reuters)

Cao Ri and Xu Jiaqian have a wedding photograph taken in a pool at the Qianyishi Underwater Photography Studio in Beijing, China on September 7, 2017. (Photo by Thomas Peter/Reuters)

New Orleans police officers try to keep their heads down as they move in on a Black Panther headquarters during an exchange of gunfire in New Orleans on September 15, 1970. The shootout occurred as police moved in to make arrests on Tuesday morning following a series of incidents. (Photo by Jack Thornell/AP Photo)