Here is an example of proportional response: Iran twice attacked Israel with missiles, the second time aiming for Tel aviv and Jerusalem. But for the Iron Dome and the US military, there would have been catastrophic damage. A proportional response to this is one that inflicts massive harm and damage to Iran's military, financial, and political strengths. Destroying their ability to produce and sell oil, wiping out the nuclear sites, hitting key military and intelligence headquarters, all qualify as severe and proportional responses that minimize civilian casualties.