A U.S. military vehicle drives past an oil pump jack in the countryside of Syria's northeastern city of Qamishli. President Trump is leaving some U.S. troops in Syria, with the goal of controlling Syria's oil fields. But legal experts say exploiting the oil could amount to pillaging — a war crime. Delil Souleiman/AFP/Getty Images hide caption

Mazloum Abdi, commander-in-chief of the Syrian Democratic Forces speaks to reporters near the northeastern Syrian Hassakeh province on Thursday. AFP via Getty Images hide caption

Actress Lori Loughlin and husband Mossimo Giannulli exit the Boston federal courthouse after a hearing on August 27. Joseph Prezioso/AFP/Getty Images hide caption

In this Oct. 23, 2018 file photo, Defense Secretary Jim Mattis speaks beside President Donald Trump, during a briefing with senior military leaders in the Cabinet Room at the White House in Washington. Manuel Balce Ceneta/AP hide caption

Ukraine's prosecutor general, Ruslan Ryaboshapka, announced Friday that he will review cases involving Hunter Biden but that he isn't aware of any evidence of wrongdoing by Biden. Valentyn Ogirenko/Reuters hide caption

Reps. Adam Smith, D-Wash. (left) and Mac Thornberry, R-Texas, are seen before a House Armed Services Committee hearing in March. Tom Williams/CQ-Roll Call, Inc via Getty Images hide caption

The inmate population at the U.S. military prison in Guantánamo Bay, Cuba, once stood at nearly 700 but has since dwindled to 40. Sylvie Lanteaume/AFP/Getty Images hide caption

Wreckage described by Saudi defense officials as coming from the airstrikes on the Abqaiq oil refinery. Bloomberg via Getty Images hide caption

James Mattis, then U.S. secretary of defense, leaves a news conference following a meeting about U.S.-China diplomacy and security at the State Department in Washington, D.C., in June 2017. Mattis' new book, Call Sign Chaos, implies criticism of President Trump without taking direct shots at him. Andrew Harrer/Bloomberg via Getty Images hide caption