Thousands of people protested the arrest of Istanbul's mayor Ekrem Imamoglu outside city hall in Istanbul on Thursday. Turkish police on Wednesday arrested Imamoglu — a popular opposition leader and key rival of President Recep Tayyip Erdogan — and several other prominent figures as part of investigations into alleged corruption and terror links. It's being seen by critics as a dramatic escalation in a crackdown on the opposition and dissenting voices in Turkey.