Marc Rich was pardoned while a fugitive for much more serious crimes.

there is no such constitutional restriction. A pardon can be issued for crimes that are not even known to have occurred or are purely imagined.

Richard Nixon would like a word with you.

You can definitely get pardoned before getting convicted. Trump pardoned Stephen Bannon after he got indicted wire fraud and money laundering, so he never went to trial for that.

https://www.forbes.com/sites/alisondurkee/2021/05/25/steve-b...

The pardon power seems to be very broad, and is most likely constrained by politics more than by statute. Set aside the idle speculation about a president pardoning themselves, pardons have been granted to whole classes of people for crimes you have yet to be charged with. Consider Jimmy Carter pardoning draft dodgers or Abraham Lincoln pardoning soldiers who fought for the Confederate army.

Absolutely. But if we're going to give our president a power that could be used too liberally, it's good that it's the power to let people go free instead of the power to imprison (or worse) anyone for anything he wishes.

Assange wasn't pardoned. He agreed to a deal to plead guilty with retroactive detention which meant no additional imprisonment.

A pardon can cover previous crimes with or without conviction.

He is getting a conviction. This is a plea deal. He will be admitting to the crime of conspiracy after which he will be a convicted by the court. He will then be a convicted felon and could be pardoned, but I doubt that is really an option. (Not 100% on the felony thing, I haven't seen how this is being charged.)