While touring Britain, Barack Obama publicly admonished the Brits for entertaining the idea of exiting the European Union in what is affectionately known as "Brexit" in that country. He said that any trade negotiations between Britain and the United States would "go to the end of the queue". In other words, we would deal with everyone else first before dealing with Britain.
A lot of Brits didn't appreciate that statement, nor his attempted meddling in Britain's affairs. Like a lot of things Obama does It could easily have a negative effect by hurting our trade with Britain. Some may simply stop buying U.S. goods in retaliation; putting us at the back of the queue. It already may have backfired since more Brits now seem to be supporting Brexit than before his remarks. Nice going, Barry!
Barack Obama's trade threat to Britain has increased support for Brexit as a string of polls show voters are ignoring the US President's claims: http://www.dailymail.co.uk/news/article-3559099/David-Cameron-s-election-guru-accuses-pro-EU-campaign-celebrating-victory-Obama-s-threats-trade-warns-s-soon-bunting.html