BERLIN, GERMANY - NOVEMBER 18: German Chancellor Angela Merkel greets British Prime Minister Theresa May upon her arrival for talks with European leaders at the Chancellery on November 18, 2016 in Berlin, Germany. May and Merkel will hold talks with French President Francois Hollands, Italian Prime Minister Matteo Renzi, Spanish Prime Minister Mariano Rajoy and U.S. President Barack Obama today on Obama's last trip to Europe as U.S. President. (Photo by Alexander Koerner/Getty Images)

BERLIN, GERMANY - NOVEMBER 18: German Chancellor Angela Merkel greets British Prime Minister Theresa May upon her arrival for talks with European leaders at the Chancellery on November 18, 2016 in Berlin, Germany. May and Merkel will hold talks with French President Francois Hollands, Italian Prime Minister Matteo Renzi, Spanish Prime Minister Mariano Rajoy and U.S. President Barack Obama today on Obama's last trip to Europe as U.S. President. (Photo by Alexander Koerner/Getty Images)

BERLIN, GERMANY - NOVEMBER 18: German Chancellor Angela Merkel (R) greets British Prime Minister Theresa May upon her arrival for talks between U.S. President Barack Obama and western European leaders at the Chancellery on November 18, 2016 in Berlin, Germany.Obama and Merkel will hold talks with British Prime Minister Theresa May, French President Francois Hollande, Italian Prime Minister Matteo Renzi and Spanish Prime Minister Mariano Rajoy today on Obama's last trip to Europe as U.S. President. (Photo by Sean Gallup/Getty Images)

BERLIN, GERMANY - NOVEMBER 18:  German Chancellor Angela Merkel (R) greets British Prime Minister Theresa May upon her arrival for talks between U.S. President Barack Obama and western European leaders at the Chancellery on November 18, 2016 in Berlin, Germany.Obama and Merkel will hold talks with British Prime Minister Theresa May, French President Francois Hollande, Italian Prime Minister Matteo Renzi and Spanish Prime Minister Mariano Rajoy today on Obama's last trip to Europe as U.S. President.  (Photo by Sean Gallup/Getty Images)

Theresa May, U.K. prime minister, looks on during a news conference with Germany's Chancellor Angela Merkel at the Chancellery in Berlin, Germany, on Friday, Nov. 18, 2016. A smooth Brexit is in the interests of the U.K., Germany and all Britain's partners, May said. Photographer: Krisztian Bocsi/Bloomberg via Getty Images

Theresa May, U.K. prime minister, looks on during a news conference with Germany's Chancellor Angela Merkel at the Chancellery in Berlin, Germany, on Friday, Nov. 18, 2016. A smooth Brexit is in the interests of the U.K., Germany and all Britain's partners, May said. Photographer: Krisztian Bocsi/Bloomberg via Getty Images

BERLIN, GERMANY - NOVEMBER 18: German Chancellor Angela Merkel (R) and British Prime Minister Theresa May give statements to the media prior to bilateral talks as the Reichstag is visible behind at the Chancellery on November 18, 2016 in Berlin, German. The two are meeting at the tail end of talks today between U.S. President Barack Obama and five western European leaders. (Pool Photo by Sean Gallup/Getty Images)

BERLIN, GERMANY - NOVEMBER 18:  German Chancellor Angela Merkel (R) and British Prime Minister Theresa May give statements to the media prior to bilateral talks as the Reichstag is visible behind at the Chancellery on November 18, 2016 in Berlin, German. The two are meeting at the tail end of talks today between U.S. President Barack Obama and five western European leaders.  (Pool Photo by Sean Gallup/Getty Images)

Theresa May, U.K. prime minister, left, and Angela Merkel, Germany's chancellor, depart a news conference at the Chancellery in Berlin, Germany, on Friday, Nov. 18, 2016. A smooth Brexit is in the interests of the U.K., Germany and all Britain's partners, May said. Photographer: Krisztian Bocsi/Bloomberg via Getty Images

Theresa May, U.K. prime minister, left, and Angela Merkel, Germany's chancellor, depart a news conference at the Chancellery in Berlin, Germany, on Friday, Nov. 18, 2016. A smooth Brexit is in the interests of the U.K., Germany and all Britain's partners, May said. Photographer: Krisztian Bocsi/Bloomberg via Getty Images