Where you are from, can you go around trying to pick locks on front doors and are only prosecuted if you succeed? And the same with cars?
I'm only critizing the analogy, what he did, or tried is still illegal but it's barely a hack attempt and it's obvious they are desperate to charge him with anything, no matter how small the charge.
They guy who drives the getaway car is guilty of murder as much as the people who walk into the building.
This is the entire point of conspiracy law. Driving a car is not a crime! But it is if you're conspiring with other people who are committing crimes. Otherwise, you would be able to take part in a murder and be let off, because all you did was act as lookout.
If you and a friend plan to poison someone, and you buy the poison and give it to your friend who then poisons the target, you are guilty of conspiracy to murder, even though buying the poison may not actually be a crime. Prosecutors may legitimately not have anything else on you because that's "all" you did!
You don't need to invent scenarios, you can use the facts of this case.
Manning already had access and didn't need the password to be cracked. Wikileaks already received information from Manning. Someone in the chat log told Manning they would pass the hash to someone else. They then told Manning "no luck so far".
Keep in mind, they haven't provided any proof that the person Manning was talking to was Assange. They haven't provided any proof that Assange did in fact try to crack it He never wrote that he would try, only that he would pass it on. Or that he actually send the hash to someone else to crack it, and that this person did in fact tried to crack it.
And to top it all off, Manning did not need the password in the first place! People keep forgetting this. The case against Assange appears to be very weak and is probably only intended to get him on US soil to question him about things other than what he is charged with.