Mark 11:18

And the chief priests and the scribes heard it, and sought how they might destroy him: for they feared him, for all the multitude was astonished at his teaching.

Note that it is not stated here that they "decided" to destroy him; that decision had already been made more than three years previously (John 5:18). Furthermore, Jesus, at the first cleansing, had associated his action with a veiled prophecy of his death and resurrection (John 2:19). Without doubt, Jesus' action in the two cleansings was a prime source of the motivation of the enemies who decided to destroy him. The principal concern of the chief priests, as revealed here, was exactly how they could bring about his death. Mark's very next verse suggests the possibility that they might have assassinated Jesus if he had not withdrawn from the city every night. That they really preferred secret murder to any public act against him is plain from Matthew 26:4.