Three years after promising a referendum, Prime Minister David Cameron announced in late February that Britain will go to the polls on June 23 to answer the question: "Should the United Kingdom remain a member of the European Union or leave the European Union?" If voters opt to leave, it will have profound consequences not only for the UK but for the EU and transatlantic relations. The EU is already embattled and a divorce with its second-largest economy and second most populous member state - albeit one which has always had a troubled relationship with the bloc - could inflict grave damage. The US has declared a "profound interest" in a very strong UK staying in a strong EU. Within Britain, the debate is already fierce and being fought on five main fronts: Migration, the economy, security, Britain's global influence and sovereignty.