They may have a plan that includes an untold number of "provisional votes". Unregistered voters, in CA anyway, can cast a "provisional ballot" if they aren't listed on the voter rolls. Under some circumstance, these are counted. Should that occur, the number of pre-election registered voters no longer limits the outcome.
But those provisional votes still face a statistical limit. Everybody assumes CA will go blue, and - as Hillary realized far too late - more votes in an already-won state mean nothing.
Yeah they might be able to turn it into a mud fight. I’m noting that’sa big enough Trump margin in the right areas mean an objective outright win, and looks like he’ll manage to get it.