Welcome to the 'rules-based' world order.
Any intelligence leak that compromises US geopolitical strategy and/or reflects negatively on US foreign policy is a crime that is punishable by death, even if the leak is made by a non-US citizen. Freedom of speech and information is only reserved for exposés by the US and its allies on their enemies.
The US administration does not want to charge Assange. They want him dead. He'll be shot down the day he's extradited and sets foot on American soil.