GOP wants Bernie to win. Bernie & Co. are too dumb to understand why, but either way, GOP voters could make the difference.
They knew since GOP had an incumbent, there would be a coordinated effort to have Republicans cross over to elevate Bernie so Trump would win in a landslide.
I'm sure the Bernie campaign encouraged this.
DNC should have anticipated this but they were so eager to appease Bernie's minions in the spirit of "unity" they obvs didn't take it into consideration.
Except this has been going on under the radar for months.