National flags of the U.S. and Germany and a NATO flag flutter in the wind near the main gate of the U.S. Spangdahlem Air Base near Bitburg, western Germany, July 30, 2020. REUTERS/Wolfgang Rattay 

Germany's Chancellor Angela Merkel looks at U.S. President Donald Trump after the family picture at the NATO leaders summit in Watford, Britain December 4, 2019. REUTERS/Yves Herman TPX IMAGES OF THE DAY 

The U.S. President Donald Trump's Cadillac limousine, also known as "The Beast", departs after the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts during a bilateral meeting with Italian Prime Minister Giuseppe Conte on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump gestures during a bilateral meeting with Italian Prime Minister Giuseppe Conte on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump and Italian Prime Minister Giuseppe Conte hold a bilateral meeting on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks as U.S. Defense Secretary Mark Esper and Acting White House Chief of Staff Mick Mulvaney look on during a bilateral meeting with Italian Prime Minister Giuseppe Conte on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks during a bilateral meeting with Italian Prime Minister Giuseppe Conte on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks during a bilateral meeting with Italian Prime Minister Giuseppe Conte on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump and Italian Prime Minister Giuseppe Conte shake hands as they hold a bilateral meeting on the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

NATO Secretary General Jens Stoltenberg looks on as U.S. President Donald Trump and Poland's President Andrzej Duda talk during a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts next to NATO Secretary General Jens Stoltenberg as they attend a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump stands among other leaders as he attends a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, near London, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts next to NATO Secretary General Jens Stoltenberg as they attend a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts next to NATO Secretary General Jens Stoltenberg as they attend a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts next to NATO Secretary General Jens Stoltenberg as they attend a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump gestures next to NATO Secretary General Jens Stoltenberg as they attend a working lunch during the NATO leaders summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump and Britain's Prime Minister Boris Johnson attend the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. Jeremy Selwyn/Pool via REUTERS 

U.S. President Donald Trump speaks during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump reacts during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump attends a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump talks with Canada's Prime Minister Justin Trudeau during a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque TPX IMAGES OF THE DAY 

U.S. President Donald Trump speaks during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks as U.S. Secretary of State Mike Pompeo and U.S. Defense Secretary Mark Esper look on during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump speaks as U.S. Secretary of State Mike Pompeo, U.S. Defense Secretary Mark Esper and Acting White House Chief of Staff Mick Mulvaney look on during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

Germany's Chancellor Angela Merkel looks on during a bilateral meeting with U.S. President Donald Trump at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump and Germany's Chancellor Angela Merkel hold a bilateral meeting at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump is seen during a bilateral meeting with Germany's Chancellor Angela Merkel at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump and Germany's Chancellor Angela Merkel hold a bilateral meeting at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. President Donald Trump shakes hands with Germany's Chancellor Angela Merkel during a bilateral meeting at the sidelines of the NATO summit in Watford, Britain, December 4, 2019. REUTERS/Kevin Lamarque 

U.S. first lady Melania Trump visits the Salvation Army Clapton centre, as the NATO summit takes place in Watford, in London, Britain, December 4, 2019. REUTERS/Lisi Niesner 

U.S. first lady Melania Trump prepares Christmas decorations with children as she visits the Salvation Army Clapton centre, as the NATO summit takes place in Watford, in London, Britain, December 4, 2019. REUTERS/Lisi Niesner 

U.S. first lady Melania Trump smiles as she visits the Salvation Army Clapton centre, as the NATO summit takes place in Watford, in London, Britain, December 4, 2019. REUTERS/Lisi Niesner 

NATO Secretary General Jens Stoltenberg and Britain's Prime Minister Boris Johnson greet U.S. President Donald Trump at the annual NATO heads of government summit at the Grove hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. first lady Melania Trump and Suzanne Johnson, wife of the US ambassador to Britain, listen to a children choir after joining local school students and U.S. Marines stationed at the U.S. Embassy, wrapping holiday presents to be donated to the Salvation Army, at the Salvation Army Clapton Center in London, Britain, December 4, 2019. Alastair Grant/Pool via REUTERS 

NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump, Germany's Chancellor Angela Merkel, Turkey's President Tayyip Erdogan and other NATO Alliance leaders leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. first lady Melania Trump and Suzanne Johnson, wife of the US ambassador to Britain, listen to a children choir after joining local school students and U.S. Marines stationed at the U.S. Embassy, wrapping holiday presents to be donated to the Salvation Army, at the Salvation Army Clapton Center in London, Britain, December 4, 2019. Alastair Grant/Pool via REUTERS 

U.S. first lady Melania Trump joins local school students and U.S. Marines stationed at the U.S. Embassy, wrapping holiday presents to be donated to the Salvation Army, at the Salvation Army Clapton Center in London, Britain, December 4, 2019. Alastair Grant/Pool via REUTERS 

U.S. first lady Melania Trump poses with a children choir after joining local school students and U.S. Marines stationed at the U.S. Embassy, wrapping holiday presents to be donated to the Salvation Army, at the Salvation Army Clapton Center in London, Britain, December 4, 2019. Alastair Grant/Pool via REUTERS 

NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump, Germany's Chancellor Angela Merkel, Turkey's President Tayyip Erdogan and other NATO Alliance leaders leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump, Turkey's President Tayyip Erdogan, Britain's Prime Minister Boris Johnson and other NATO Alliance leaders leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump and Turkey's President Recep Tayyip Erdogan leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. first lady Melania Trump joins local school students and U.S. Marines stationed at the U.S. Embassy, wrapping holiday presents to be donated to the Salvation Army, at the Salvation Army Clapton Center in London, Britain, December 4, 2019. Alastair Grant/Pool via REUTERS 

U.S. President Donald Trump, Turkey's President Tayyip Erdogan, France's President Emmanuel Macron and Germany's Chancellor Angela Merkel pose for a family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump and Turkey's President Tayyip Erdogan pose for a family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump, Turkey's President Tayyip Erdogan, France's President Emmanuel Macron and Germany's Chancellor Angela Merkel pose for a family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump and Turkey's President Tayyip Erdogan pose for a family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

Britain's Prime Minister Boris Johnson welcomes U.S. President Donald Trump at the NATO leaders summit in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

NATO Secretary General Jens Stoltenberg, U.S. President Donald Trump, Britain's Prime Minister Boris Johnson, Turkey's President Tayyip Erdogan and other NATO Alliance leaders leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump, Germany's Chancellor Angela Merkel, Italian Prime Minister Giuseppe Conte and other NATO Alliance leaders leave the stage after family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

NATO Secretary General Jens Stoltenberg and Britain's Prime Minister Boris Johnson greet U.S. President Donald Trump at the annual NATO heads of government summit at the Grove hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

NATO Secretary General Jens Stoltenberg and Britain's Prime Minister Boris Johnson greet U.S. President Donald Trump at the annual NATO heads of government summit at the Grove hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

NATO Secretary General Jens Stoltenberg and Britain's Prime Minister Boris Johnson greet U.S. President Donald Trump at the annual NATO heads of government summit at the Grove hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump and Germany's Chancellor Angela Merkel pose for the family photo during the annual NATO heads of government summit at the Grove Hotel in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

Britain's Prime Minister Boris Johnson welcomes U.S. President Donald Trump at the NATO leaders summit in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

Britain's Prime Minister Boris Johnson and U.S. President Donald Trump attend at the NATO leaders summit in Watford, Britain December 4, 2019. REUTERS/Peter Nicholls/Pool 

U.S. President Donald Trump, U.S. Secretary of State Mike Pompeo and Acting White House Chief of Staff Mick Mulvaney look on as they attend a North Atlantic Treaty Organization Plenary Session at the NATO summit in Watford, near London, Britain, December 4, 2019. REUTERS/Kevin Lamarque