They can't trade Charles. No one would take the salary on with the risk. Look at what is happening in GB. they will keep nursing Charles back to health as the season progresses. Ware is still the main guy for now.
With regard to Charles' salary, here is the info per
spotrac.
Assuming this is accurate, if a team trades for him now, it would be on the hook for only the remainder of his $2.75M salary this season -- less than $2M. The Chiefs would take the hit on their cap for his roster and workout bonuses for 2016, which should have already come due and been paid.
Neither the Chiefs nor any team trading for Charles is on the hook for any dead cap hit if they release him after this season. If the team that has him keeps him for 2017, it will come with a $7M cap hit, unless that team gets Charles to restructure to a lower but mutually acceptable cap hit.
So a team could trade for him, pay him a relatively reasonable salary for the rest of 2016, given the potential upside, and use that period as an audition for what to do with him in 2017.
I'm not saying the Chiefs should trade him, since they could potentially be a playoff contender. I'm also not saying he is a nobrainer for another team to target in a trade. But I don't think his contract is the problem it has been made out to be in this thread. If there is a RB needy team that feels that Charles could be a difference maker down the stretch, has a couple $M in cap room, and can negotiate a reasonable trade, I could see it happening.
I don't see having Charles in addition to Ware and West as making a non-trivial difference in KC's playoff chances this season, and I think KC will likely release Charles after the season. So they could easily be motivated to get something for him if other teams are interested.
