Stephen Sackur speaks to Bulgaria's foreign minister, Daniel Mitov. If a chain is only as strong as its weakest link, then the European Union has reason to worry about Bulgaria. Once a redoubt of the Soviet Empire, Bulgaria is by many measures the poorest, most corrupt member of the European Union. It also happens to be a key player in two of the great challenges facing the EU, the migration crisis and the hostile relationship with Russia. Can Brussels rely on Bulgaria?