After a freezing night out in the open, hundreds of striking Serbian students have resumed their 2-day anti-graft protest march from the capital, Belgrade to the northern city of Novi Sad. They plan to blockade three bridges over the River Danube this weekend, marking three months since a huge concrete construction at the railway station in Novi Sad collapsed on Nov. 1, leaving 15 people dead. What started two months ago as a protest against suspected corruption in construction contracts has developed into the most serious challenge in years to the country’s powerful populist leader, President Aleksandar Vucic.