President Barack Obama and First Lady Michelle were in London bearing gifts today for Queen Elizabeth’s 90th birthday celebration. The Obamas brought her a photo album with snapshots of her visits with American presidents and first ladies.

But the president wasn’t just there to give birthday wishes. He also had a message for regular British citizens: Please don't leave the European Union. They vote on that in June.

“The United States wants a strong United Kingdom as a partner. And the United Kingdom is at its best when it’s helping to lead a strong Europe,” Obama said in London.

Many Brits who favor the UK's exit — known as “Brexit” — from the 28-nation bloc were unhappy with Obama’s strong tone.

“This wasn’t the sort of careful, tip-toeing and diplomatic fiddling about that you might have expected on some occasions,” said the BBC’s Rob Watson. “This was a really full-throated, direct, absolutely unambiguous endorsement for Britain’s membership in the European Union.”   

London’s mayor Boris Johnson, who favors Brexit, said President Obama may have an “ ancestral dislike of the British empire.” When Johnson was later asked if he intended to imply that Obama was anti-British, Johnson replied, “Not at all. Not at all.”

Still, many in the pro-EU camp weren’t letting London's mayor off quite so easily.

“Lots of people on the ‘stay' side latched onto it and said, ‘Whoa, there’s a really big whiff of racisim about this,” said Watson.

British Prime Minister David Cameron, the unoffical head of the stay-in-the-EU camp, knows the impact Obama's visit and his pro-EU message could have in his country and on undecided voters. Opinion polls suggest Obama is more popular in the UK than almost any British politician.

“[Cameron] will hope that people switching on their evening news in Britain tonight will say, 'Well, you know, President Obama ... doesn’t think it’s a good idea that we should leave, maybe I’ll give it a second thought,'” said Watson.

From PRI's The World ©2016 PRI