 Complete the following phrase:  A professor of political economy at Sofia University from 1910 onwards, he took a leading role in the overthrow of the government of Aleksandar Stamboliyski in 1923 and was chosen to head the coalition that succeeded the deposed premier. The coup was able to succeed as the Bulgarian Communist Party took a neutral attitude towards the Agrarians rather than supporting Stamboliyski. He became Prime Minister of Bulgaria on 9 June that same year and continued in the role until 4 January 1926. During that period he was the leader of the Democratic Alliance. His premiership was marked by deep internal struggles with the Bulgarian Communist Party, which Tsankov repressed mercilessly, declaring martial law and outlawing the Communists in 1925 following an attempt on Tsar Boriss life and a 