Offering an opinion. As a friend. That, said Barack Obama at his press conference in the Foreign Office, was all he was doing.
"You shouldn't be afraid to hear an argument being made," he said. "It's not a threat." He said it so calmly, so casually - indeed, so charmingly - that you could easily have believed it.
And he was speaking just as calmly, casually and charmingly less than a minute later when he said that if the UK thought it would get a free trade deal with the US after Brexit, it was frankly dreaming.
There would be no such deal "any time soon", he explained. America was quite busy enough working on a trade deal with the EU, thanks very much. If the UK wanted a trade deal of its own, it would have to make do with waiting "at the back of the queue".
Leaving aside, for a moment, the obvious political impact of that crushing dismissal: note the language. He said "queue". Not "line", as Americans call it. "Queue", as Britons call it.
The President was answering a question from a journalist, but he wasn't talking off the top of his head.
He'd planned that line, and phrased it with care: this was a phrase he wanted to see printed on British front pages, and heard on British news bulletins, and understood instantly by every British voter.
You want to leave the EU and still be our friend? Back of the queue, Britain. Back of the queue. No matter how Brexit campaigners frame their response - whether indignant, stout or mocking - this will have hurt them.
Of course Obama won't be in the White House for much longer; his replacement will be along soon. But so much of their argument has rested on the breeziness with which they have assured voters that Britain could do a deal with the US both successfully and swiftly.
Here was the US President, shaking his head in wry amusement and then strolling away, chuckling.
Prime Minister David Cameron couldn't have looked happier. He gazed at the President with almost touching gratitude.
"I'm honoured to have Barack as a friend," he simpered, girlishly. "I'm very proud to have had the opportunity to be Prime Minister and to stand outside the White House, listening to this man, my friend Barack, say that the special relationship between our countries has never been stronger."
He liked to think, he added, that the two of them had "got to know each other pretty well".
Perhaps - although not quite well enough, it seems, to know how to pronounce his good friend's name. Even after six years of their friendship, Cameron is still saying Buh-RACK, rather than Buh-RAHK.
It says a lot for the special relationship that Obama has never embarrassed him by pointing out his mistake.
Then again, Obama did mention that he'd enjoyed visiting "the Duke of Edinboro", so I suppose we'll call it even.