US President Donald Trump (C) greets Jordan's King Abdullah II (R) during a luncheon at the United Nations headquarters during the 72nd session of the United Nations General Assembly September 19, 2017 in New York City. / AFP PHOTO / Brendan Smialowski (Photo credit should read BRENDAN SMIALOWSKI/AFP/Getty Images)
US President Donald Trump (L) congratulates Senior Counselor to the President Stephen Bannon during the swearing-in of senior staff in the East Room of the White House on January 22, 2017 in Washington, DC. / AFP / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images)
WASHINGTON, DC - APRIL 26: After answering questions from reporters, Sen. John McCain departs the U.S. Capitol for a briefing on North Korea at the White House April 26, 2017 in Washington, DC. Members of U.S. President Donald Trump's national security team held a briefing on North Korea at the White House for the entire U.S. Senate. (Photo by Win McNamee/Getty Images)
South Korea's Defense Minister Han Min-Koo (L) shows US Pentagon chief Jim Mattis (C) how to pose for a tri-handshake, as Japan's Defence Minister Tomomi Inada looks on, during a trilateral meeting on the sidelines of the 16th Institute for Strategic Studies (IISS) Shangri-La Dialogue Summit in Singapore on June 3, 2017.
The annual Shangri-La Dialogue is attended by defence ministers from around the region and runs from June 2 to 4. / AFP PHOTO / Roslan RAHMAN (Photo credit should read ROSLAN RAHMAN/AFP/Getty Images)
ALEXANDRIA, VA - MARCH 29: Federal Bureau of Investigation Director James Comey delivers the keynote remarks at the Intelligence and National Security Alliance Leadership Dinner March 29, 2017 in Alexandria, Virginia. While testifying before the House Intelligence Committee last week, Comey said the FBI is investigating the Trump campaign's ties to Russia, and will pursue it "no matter how long that takes." (Photo by Chip Somodevilla/Getty Images)
WASHINGTON, DC - APRIL 11: US President Donald Trump speaks during a strategic and policy discussion with CEOs in the State Department Library in the Eisenhower Executive Office Building (EEOB) on April 11, 2017 in Washington, DC. (Photo by Olivier Douliery-Pool/Getty Images)
TOPSHOT - US President Donald Trump delivers a statement on Syria from the Mar-a-Lago estate in West Palm Beach, Florida, on April 6, 2017.
Trump ordered a massive military strike against a Syria Thursday in retaliation for a chemical weapons attack they blame on President Bashar al-Assad. A US official said 59 precision guided missiles hit Shayrat Airfield in Syria, where Washington believes Tuesday's deadly attack was launched.
/ AFP PHOTO / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
US Defense Secretary James Mattis waits for the arrival of Saudi Deputy Crown Prince and Defense Secretary Mohammed bin Salman at the Pentagon in Washington, DC, on March 16, 2017. / AFP PHOTO / NICHOLAS KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
NEWPORT NEWS, VA - MARCH 02: U.S. President Donald Trump speaks to members of the U.S. Navy and shipyard workers on board the USS Gerald R. Ford CVN 78 that is being built at Newport News shipbuilding, on March 2, 2017 in Newport News, Virginia. The USS Ford is powered by two Nuclear reactors and is 1, 092 feet long with a 134 foot beam and can carry over 75 aircraft. (Photo by Mark Wilson/Getty Images)
US Vice-President Mike Pence gestures as he speaks during a press conference after their meeting at NATO headquarters in Brussels on February 20, 2017.
US President Donald Trump expects NATO allies to make real progress by the end of this year towards the increased defence spending target agreed by the alliance, his Vice President Mike Pence said on February 20, 2017. / AFP / EMMANUEL DUNAND (Photo credit should read EMMANUEL DUNAND/AFP/Getty Images)
US President-elect Donald Trump (L) stands with Trump National Security Adviser Lt. General Michael Flynn (R) at Mar-a-Lago in Palm Beach, Florida, where he is holding meetings on December 21, 2016. / AFP / JIM WATSON (Photo credit should read JIM WATSON/AFP/Getty Images)
US Secretary of Defence James Mattis addresses a press conference following the NATO Defence Ministers' meeting at the NATO headquarters in Brussels, on February 16, 2017.
The US military is not yet ready to cooperate with Russia, Pentagon chief James Mattis said on February 16 after Moscow's defence minister called for better ties. "We are not in a position right now to collaborate on a military level, but our political leaders will engage and try to find common ground or a way forward," Mattis told reporters at the NATO summit in Brussels.
/ AFP / THIERRY CHARLIER (Photo credit should read THIERRY CHARLIER/AFP/Getty Images)
WASHINGTON, DC - JANUARY 28: President Donald Trump signs three executive actions in the Oval Office on January 28, 2017 in Washington, DC. The actions outline a reorganization of the National Security Council, implement a five year lobbying ban on administration officials and a lifetime ban on administration officials lobbying for a foreign country and calls on military leaders to present a report to the president in 30 days that outlines a strategy for defeating ISIS. (Photo by Pete Marovich - Pool/Getty Images)
WASHINGTON, DC - JANUARY 19: (AFP OUT) President-elect Donald J. Trump and wife Melania Trump arrive for the inaugural concert at the Lincoln Memorial in January 19, 2017 in Washington, DC. Hundreds of thousands of people are expected tomorrow for Trump's inauguration as the 45th president of the United States. (Photo by Chris Kleponis-Pool/Getty Images)
Activists display a photo of US President Barack Obama (L) and pictures of former US spy Edward Snowden (C) and whistleblower Bradley Manning (R) during a protest action on June 19, 2013 in Berlin on behalf of the visit of the US President in the German capital. Barack Obama will walk in John F. Kennedy's footsteps this week on his first visit to Berlin as US president, but encounter a more powerful and sceptical Germany in talks on trade and secret surveillance practices.. AFP PHOTO / RONNY HARTMANN