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.
Operation Priboi Operation Priboi ("Coastal Surf") was the code name for the Soviet mass deportation from the Baltic states on 25–28 March 1949. The action is also known as the March deportation by Baltic historians. More than 90,000 Estonians, Latvians and Lithuanians, labeled as enemies of the people, were deported to forced settlements in inhospitable areas of the Soviet Union. Over 70% of the deportees were women, and children under the age of 16.