During Slutsky's tenure, the Foreign Department was principally engaged in tracking down and eliminating opponents of Stalin's regime, essentially emigre White Russians and Trotskyists.

Major operations included kidnapping of General Evgenii Miller, burglary of the Trotsky archive in Paris, assassination of Ignace Reiss, and liquidation of numerous Trotskyists and anti-Stalinists in Spain during the Civil War.

The voluble Slutsky described his methods for "breaking-down" these Old Bolsheviks to his subordinates, Alexander Orlov and Walter Krivitsky, who subsequently recounted these episodes in their memoirs.

In character, the defector Orlov, who worked directly under him and knew him well, thought Slutsky was "distinguished by laziness, a propensity for window dressing and by subservience to his chiefs.

Elizabeth Poretsky, who met with him frequently in 1936, thought he "was a person of many contradictions ... he would weep while telling of the interrogation of some of the defendants at the trials and bemoan the fates of their families; in the same breath he would denounce them as 'Trotskyite fascists.'"

When Nikolai Yezhov assumed control of the NKVD in 1937, he began to arrest and liquidate the department heads whom he knew were close to his deposed predecessor, Yagoda.

Slutsky was spared, even though he was implicated in confessions as a "participant in Yagoda's conspiracy," because Yezhov feared that Slutky's arrest would cause Soviet agents who were operating abroad to defect.

Shortly afterward, his deputy, Sergei Shpigelglas, was called into the office and he observed Slutsky slumped in a chair with tea and cakes at the table beside him.