Denvention is scheduled for the same main facility 3 weeks earlier -- August, 6-10. One person on Denvention's facilities committee has already posted to SMOFs that they are double checking with the facility to see if this impacts the Worldcon.
While I'm not an expert on political conventions, past discussions on SMOFs and other things make me a bit worried that the DNC may want the convention center for more than 2-and-a-half weeks prior to the opening of their convention, and that their 35,000 participants will so completely dwarf Denvention's 3,000, that this may not be a good thing for the convention.
At least they weren't bidding for the weekend before Labor day
I'm going to stay tuned to SMOFs to see what develops.