British Prime Minister Theresa May, right, greets European Commission President Jean-Claude Juncker during a round table meeting at an EU summit in Brussels, Thursday, Dec. 13, 2018. EU leaders gathered Thursday for a two-day summit which will center on the Brexit negotiations. (AP Photo/Alastair Grant)

Kosovo president Hashim Thaci, center, flanked by KSF Commander Rrahman Rama as they inspect members of Kosovo Security Force in capital Pristina, Kosovo, on Thursday, Dec. 13, 2018. Kosovo lawmakers are set to transform the Kosovo Security Force into a regular army, a move that significantly heightened tension with neighboring Serbia. (AP Photo/Visar Kryeziu)

A French soldiers patrols as the Christmas market reopens in Strasbourg, eastern France, Friday, Dec.14, 2018. The man authorities believe killed three people during a rampage near a Christmas market in Strasbourg died Thursday in a shootout with police at the end of a two-day manhunt, French authorities said. (AP Photo/Christophe Ena)

FILE - In this Thursday, July 12, 2018, file photo, the container ship Maersk Emerald is unloaded at the Port of Oakland, Calif. China has announced a 90-day suspension of tariff hikes on $126 billion of U.S. cars, trucks and auto parts following its cease-fire in a trade battle with Washington that threatens global economic growth. (AP Photo/Ben Margot, File)

Polish teenagers stage a protest in the U.N. climate conference venue on the last days of talks to urge negotiators from almost 200 countries to reach an agreement on ways of keeping global warming in check in Katowice, Poland, Friday, Dec. 14, 2018. (AP Photo/Czarek Sokolowski)

People pass by a NATO-led peacekeeping force KFOR vehicle in front of the main bridge between the southern, ethnic Albanian-dominated and the northern, Serb-dominated part of Mitrovica, Kosovo, Friday, Dec. 14, 2018. Kosovo's parliament overwhelmingly approved the formation of an army, a move that has angered Serbia which says it would threaten peace in the war-scarred region. (AP Photo/Darko Vojinovic)

Sen. Bernie Sanders, I-Vt., joined at left by Sen. Chris Murphy, D-Conn., holds a news conference after the Senate passed a resolution he introduced that would pull assistance from the Saudi-led war in Yemen, a measure to rebuke Saudi Arabia after the killing of journalist Jamal Khashoggi, at the Capitol in Washington, Thursday, Dec. 13, 2018. (AP Photo/J. Scott Applewhite)

A woman is reflected on the electronic board of a securities firm in Tokyo, Friday, Dec. 14, 2018. Asian markets tumbled on Friday after China reported weaker-than-expected economic data, stirring up worries about the state of the world's second largest economy. (AP Photo/Koji Sasahara)

British Prime Minister Theresa May arrives for an EU summit in Brussels, Friday, Dec. 14, 2018. European Union leaders have offered Theresa May sympathy but no promises, as the British prime minister seeks a lifeline that could help her sell her Brexit divorce deal to a hostile U.K. Parliament. (AP Photo/Alastair Grant, Pool)