White House Chief of Staff John Kelly carries his briefcases to board Air Force One with U.S. President Trump for travel to New Jersey from Joint Base Andrews, Maryland, U.S. August 4, 2017. REUTERS/Jonathan Ernst

U.S. President Donald Trump turns to White House Chief of Staff John Kelly during a visit with U.S. Marines at the Marine Corps Barracks in Washington, U.S. November 15, 2018.

U.S. President Donald Trump (C), flanked by Vice President Mike Pence (L) and Homeland Security Secretary John Kelly (R), takes the stage to deliver remarks at Homeland Security headquarters in Washington, U.S. January 25, 2017.

White House Chief of Staff John Kelly listens as U.S. President Donald Trump takes part in a working lunch with governors in the Roosevelt Room at the White House in Washington, U.S., June 21, 2018.

Senior White House Advisor Jared Kushner, Senior White House Advisor Ivanka Trump and White House Chief of Staff John Kelly follow U.S. President Donald Trump and U.S. first lady Melania Trump as they walk to Marine One as they depart for Pittsburgh from the South Lawn of the White House in Washington, U.S., October 30, 2018.

White House Chief of Staff John Kelly stands before a Medal of Honor ceremony in the East Room of the White House in Washington, U.S., July 31, 2017.

White House Chief of Staff John Kelly looks walks past tombstones during a ceremony at the Aisne-Marne American Cemetery dedicated to the U.S. soldiers killed in the Belleau Wood battle during World War One at Belleau, France, November 10, 2018.

White House Chief of Staff John Kelly waits behind the Resolute Desk as U.S. President Donald Trump delivers remarks to reporters as he welcomes United Nations Secretary General Antonio Guterres for a meeting in the Oval Office at the White House in Washington, U.S. October 20, 2017.

U.S. President Donald Trump shakes hands with John Kelly after he was sworn in as White House Chief of Staff in the Oval Office of the White House in Washington, U.S., July 31, 2017.

White House Chief of Staff John Kelly looks on as U.S. President Donald Trump speaks to reporters in the Oval Office at the White House in Washington, U.S. February 9, 2018.

U.S. Ambassador to the United Nations Nikki Haley shows White House Chief of Staff John Kelly and Secretary of State Mike Pompeo papers and a handwritten note reading: "After you thank the Prime Minister of the Netherlands, you can depart. I will take the chair. You don't need to say anything further" that she had just showed to U.S. President Donald Trump as he chaired a UN Security Council meeting during the 73rd session of the United Nations General Assembly at U.N. headquarters in New York, U.S., September 26, 2018.

White House Chief of Staff John Kelly (2nd L) wipes his eyes while seated with National Security Adviser H.R. McMaster (L) U.S. Secretary of State Rex Tillerson (2nd R) and Vice President Mike Pence as U.S. President Donald Trump holds a joint press conference with Finnish President Sauli Niinisto at the White House in Washington, U.S., August 28, 2017.

U.S. President Donald Trump flanked by Secretary of State Mike Pompeo and White House Chief of Staff John Kelly attend a lunch with Singapore's Prime Minister Lee Hsien Loong and officials at the Istana in Singapore June 11, 2018.

Homeland Security Secretary John Kelly (L), Secretary of State Rex Tillerson (C) and Attorney General Jeff Sessions (R), deliver remarks on issues related to visas and travel after U.S. President Donald Trump signed a new travel ban order in Washington, U.S., March 6, 2017.

White House Chief of Staff John Kelly attends the news conference held by U.S. President Donald Trump following Tuesday's midterm congressional elections at the White House in Washington, U.S., November 7, 2018.

White House Chief of Staff John Kelly steps out from inside an armored vehicle as U.S. President Donald Trump participatesin a briefing on Hurricane Florence recovery efforts at Marine Corps Air Station Cherry Point in Havelock, North Carolina, U.S., September 19, 2018. REUTERS/Kevin Lamarque TPX IMAGES OF THE DAY - RC1D32CDD5D0

U.S. President Donald Trump (C), flanked by Vice President Mike Pence (L) and Homeland Security Secretary John Kelly (R), takes the stage to deliver remarks at Homeland Security headquarters in Washington, U.S., January 25, 2017.

White House Chief of Staff John Kelly looks out from behind a curtain before U.S. President Donald Trump addresses the Veterans of Foreign Wars’ 119th VFW national convention in Kansas City, Missouri, U.S., July 24, 2018.