When did the campaign of political  repression that Mikhail Demichev was arrested during occur?
Great Purge The Great Purge or the Great Terror (Russian: Большо́й терро́р ) was a campaign of political repression in the Soviet Union which occurred from 1936 to 1938. It involved a large-scale purge of the Communist Party and government officials, repression of peasants and the Red Army leadership, widespread police surveillance, suspicion of "saboteurs", "counter-revolutionaries", imprisonment, and arbitrary executions. Mobile gas vans were invented to execute people without trial. In Russian historiography, the period of the most intense purge, 1937–1938, is called Yezhovshchina (Russian: Ежовщина ; literally, "Yezhov phenomenon", commonly translated as "times of Yezhov" or "doings of Yezhov"), after Nikolai Yezhov, the head of the Soviet secret police, the NKVD, who was later killed in the purge. It has been estimated that 600,000 people died at the hands of the Soviet government during the Purge.
Bulgarian Communist Party The Bulgarian Communist Party (BCP) (Българска Комунистическа Партия, Bâlgarska Komunisticheska Partiya; БКП, BKP) was the Communist and Marxist-Leninist ruling party of the People's Republic of Bulgaria from 1946 until 1989 when the country ceased to be a communist state. The Bulgarian Communist Party had dominated the Fatherland Front coalition that took power in 1944, late in World War II, after it led a coup against Bulgaria's tsarist regime in conjunction with the Red Army's crossing the border. It controlled its armed forces, the Bulgarian People's Army.