Another event, of a political nature this time, shocked Istomin: the April 1967 coup d’état, fomented by the CIA, which feared that King Constantine would not be able to deal with the likely victory of the parties of the left in the upcoming parliamentary elections. Such a victory could result in Greece’s departure from NATO, its reconciliation with the USSR and a serious change in the balance of forces in the Mediterranean. The US 6th Fleet, which had just been driven out of France and had resettled in Italy, would have to face a much more delicate situation.
A fascist regime was established. All opponents were arrested, thrown into jail or penned up on the islands. Some were able to flee, such as Manos Hadjidakis who went into exile in New York where Istomin sheltered him for a while. A few weeks later, Istomin was scheduled to give two concerts with Isaac Stern and Leonard Rose at the Herod Atticus Theatre as part of the Athens Festival. A committee including Leonard Bernstein, Edward Albee, Jules Dassin and Melina Mercouri urged artists to cancel any participation in cultural events in Greece that could be considered as expressions of support for the fascist regime. There was a lengthy discussion at Pierre Salinger’s home, and in the end, the Trio decided to go ahead with the concerts, scheduled for June 29 and 30, while trying to express as clearly as possible their disapproval of the regime and their support for the political prisoners. Istomin endorsed this position, although he would have preferred to cancel. He subsequently made public his decision not to return to Greece under the current regime.
In 1974, once democracy was restored, Istomin received a letter of thanks from the new government for his sympathy and support, inviting him to come back to Greece as soon as possible. He quickly returned to the National Orchestra of Greece, of which Manos Hadjidakis had become the music director.