The president has publicly antagonized America's European Union allies, even describing the bloc as a "foe."
"Larry, those words came out of Boris Johnson's mouth," CNN anchor Brianna Kielar pushed back. "How do you argue with that?"
"Under no condition can we agree with this logic," European Council President Donald Tusk said.
Once negotiations begin, Theresa May's slender majority will bring new challenges.
Tusk's comments follow the British prime minister's accusations that Brussels was meddling in the U.K.'s election.
EU leadership is determined to present a united front as Theresa May seeks deals for Britain.
"After more than 40 years of being united, we owe it to each other to do everything we can to make this divorce as smooth as possible," Tusk said.
A free trade deal like Canada has with the EU would not provide the same market access British firms currently enjoy.
Triggering article 50 will begin a two-year period in which the U.K. will negotiate any future relationship with the EU.
Nation says it will obstruct business in Brussels as payback after the bloc supported Donald Tusk's leadership of the European Council.
They cited defeating ISIS and tackling climate change as shared priorities.
Robert Fico says the EU won't give in to U.K.'s demands.
The 27-nation bloc is deciding upon its future without Britain.
Historically, NATO and the EU don't normally work together, but this is changing.
EC president's top aide also said a Johnson premiership would be a "horror scenario."
The European Council president said the ex-London mayor "crossed the boundaries of a rational discourse."
Ankara would take back all illegal migrants who cross to Greece in return for the EU taking in thousands of Syrian refugees from Turkey.
The European Council President also assured Greece that Brussels would not abandon the country.
Agreement fires starting gun on British Membership Referendum