The most prominent potential challenger to Egyptian President Abdel Fattah al-Sisi in elections scheduled for December announced on Friday he would not be standing after he was unable to secure the required number of public endorsements. The campaign of Ahmed el-Tantawy, a leftist former member of parliament, said officials and pro-government thugs had prevented many people from registering their support for his candidacy while security forces had arrested dozens of his supporters and blocked hi