Jerusalem's status - as part of Israel, or Palestine, or both - has long been a controversial issue many politicians have shied away from. But President Donald Trump changed decades of US policy last week by recognising the holy city as Israel's capital. The US president's decision set off worldwide protests and condemnation. Turkish President Recep Tayyip Erdogan called a meeting of the Organisation of Islamic Cooperation on Wednesday to discuss a response. He said the US decision was illegal and a threat to all humanity. But what can the 57-member organisation realistically do to pressure the US?