Turkish authorities detained President Recep Tayyip Erdogan¡¯s top political rival on corruption charges, triggering a selloff in stocks and the lira.

Istanbul Mayor Ekrem Imamoglu, the most popular Turkish politician who could one day challenge the president¡¯s rule, was taken into custody on Wednesday, sparking protests from members of opposition parties.

The mayor¡¯s detention highlights an increasingly aggressive campaign that Erdogan is waging against critics to silence dissent. He also needs to broaden his support base in parliament to have a shot at running for office again after hitting the two-term constitutional limit. The probe against his most formidable challenger serves as a stark reminder of the risks involved in investing in Turkey, where assets posted the biggest declines worldwide.