By exerting pressure on Iran, the only way to achieve an agreement with Tehran that will constrain its clients’ activities is to exert pressure on Iran.
The only way to pressure Iran itself to come to terms with it is to restrain its own activities. The only way to impose pressure on Iran itself is to reach an agreement with Tehran to restrain the activities of its clients.
By exerting pressure on Iran, the only way to achieve an agreement with Tehran that will constrain its clients’ activities is to exert pressure on Iran.