see more

Donald Tusk, president of the European Union, speaks before an event with Jens Stoltenberg, secretary general of the North Atlantic Treaty Organisation (NATO), not pictured, in Brussels, Belgium, on Tuesday, Feb. 2, 2016. British Prime Minister David Cameron said he's proved the U.K. can wring significant changes from the EU after Tusk issued a draft proposal which includes a way to mitigate benefits to foreign workers. Photographer: Jasper Juinen/Bloomberg via Getty Images

Donald Tusk, president of the European Union, speaks before an event with Jens Stoltenberg, secretary general of the North Atlantic Treaty Organisation (NATO), not pictured, in Brussels, Belgium, on Tuesday, Feb. 2, 2016. British Prime Minister David Cameron said he's proved the U.K. can wring significant changes from the EU after Tusk issued a draft proposal which includes a way to mitigate benefits to foreign workers. Photographer: Jasper Juinen/Bloomberg via Getty Images

see more

Donald Tusk, president of the European Union, holds talks with Jens Stoltenberg, secretary general of the North Atlantic Treaty Organisation (NATO), not pictured, in Brussels, Belgium, on Tuesday, Feb. 2, 2016. British Prime Minister David Cameron said he's proved the U.K. can wring significant changes from the EU after Tusk issued a draft proposal which includes a way to mitigate benefits to foreign workers. Photographer: Jasper Juinen/Bloomberg via Getty Images

Donald Tusk, president of the European Union, holds talks with Jens Stoltenberg, secretary general of the North Atlantic Treaty Organisation (NATO), not pictured, in Brussels, Belgium, on Tuesday, Feb. 2, 2016. British Prime Minister David Cameron said he's proved the U.K. can wring significant changes from the EU after Tusk issued a draft proposal which includes a way to mitigate benefits to foreign workers. Photographer: Jasper Juinen/Bloomberg via Getty Images

see more

US President Donald Trump arrives at EU headquarters ahead of a meeting with European Council President, as part of the NATO meeting, in Brussels, on May 25, 2017. (Photo by Arne Gillis/NurPhoto via Getty Images)

US President Donald Trump arrives at EU headquarters ahead of a meeting with European Council President, as part of the NATO meeting, in Brussels, on May 25, 2017. (Photo by Arne Gillis/NurPhoto via Getty Images)

see more

Theresa May, U.K. prime minister, right, and Emmanuel Macron, France's president, walk off stage during a news conference following their U.K.-France summit meeting at the military academy in Sandhurst, U.K., on Thursday, Jan. 18, 2018. Thursday's summit between May and Macron will aim to go beyond the wrangling over the specifics of Brexit and look to what the two nations have in common. Photographer: Andy Rain/Bloomberg via Getty Images via Pool

Theresa May, U.K. prime minister, right, and Emmanuel Macron, France's president, walk off stage during a news conference following their U.K.-France summit meeting at the military academy in Sandhurst, U.K., on Thursday, Jan. 18, 2018. Thursday's summit between May and Macron will aim to go beyond the wrangling over the specifics of Brexit and look to what the two nations have in common. Photographer: Andy Rain/Bloomberg via Getty Images via Pool

see more

Theresa May, U.K. prime minister, center left, and Emmanuel Macron, France's president, center right, attend a U.K.-France summit meeting at the military academy in Sandhurst, U.K., on Thursday, Jan. 18, 2018. Thursday's summit between May and Macron will aim to go beyond the wrangling over the specifics of Brexit and look to what the two nations have in common. Photographer: Andy Rain/Bloomberg via Getty Images via Pool

Theresa May, U.K. prime minister, center left, and Emmanuel Macron, France's president, center right, attend a U.K.-France summit meeting at the military academy in Sandhurst, U.K., on Thursday, Jan. 18, 2018. Thursday's summit between May and Macron will aim to go beyond the wrangling over the specifics of Brexit and look to what the two nations have in common. Photographer: Andy Rain/Bloomberg via Getty Images via Pool