Professor Ted Malloch, the man tipped to be Donald Trump's top diplomat to the EU, sparked outrage when he said wanted to "tame" the economic and political bloc on Thursday night (26 January).
The academic, 64, even compared the EU to the communist empire of the Soviet Union, which saw the brutal oppression of political opponents and the death of tens of millions of people.
"I had in a previous career a diplomatic post where I helped to bring down the Soviet Union, so maybe there's another union that needs a little taming," he told BBC Two's This Week.
Malloch also took aim at European Commission President Jean-Claude Juncker during the exchange with veteran journalist Andrew Neil. "[He was a] very adequate mayor of some city in Luxembourg," the Trump ally quipped.
Juncker, a centre-right politician, served as prime minister of Luxemburg between 1995 and 2013. The undiplomatic language comes ahead of Theresa May's meeting with Trump in the US.
The British prime minister addressed a group of Republican politicians in Pennsylvania on Thursday. The Conservative premier argued that it was America's "destiny" to beat the leadership of the free world.
"But my country, the United Kingdom of Great Britain and Northern Ireland, has been proud to share that burden and to walk alongside you at every stage," she said.
"For the past century, Britain and America – and the unique and special relationship that exists between us – have taken the idea conceived by those "fifty-six rank-and-file, ordinary citizens", as President Reagan called them, forward.
"And because we have done so, time and again it is the relationship between us that has defined the modern world."
May is expected to discuss trade, terrorism and other issues when she meets Trump. The leaders will also hold a joint press conference, according to the White House.