Pte Manning copied very sensitive government communications and released them to 3rd part(y|ies). The individual was tried by Court Martial and found guilty on a number of charges and sentenced to 35 years imprisonment - a sentence which was later commuted to 7 years time-served.
Mr Assange is the front man for an organisation which published the information that Pte Manning supplied. He claims he fears extradition to the US where he might face the death penalty. To avoid this he has confined himself in a building in London (technically Ecuadorian territory) for more than 5 years so far.
If the person who stole the information while supposedly under military discipline got a custodial sentence then the person who published it is *not* likely to get a harsher sentence (death penalty).
Some of the *other* stuff that Mr Assange's organisation has published has certainly annoyed many more people around the world and some might see political/media advantage in hastening his death and possibly casting the blame on others. I think him going to the US would probably extend his life rather than shorten it.
Mr Assange will die - eventually. Maybe from old-age (having witnessed that recently I would not wish it on anyone) or from some form of ill-health or even by being killed. He seems to be increasing his risk of the last option.