He was like Hillary - thought it a guaranteed win. Adios, Bill.
I think you’re right on, Nelson thought it was a lock for him.
The Democrats underestimated the revulsion working class voters in Wisconsin, Michigan, and Pennsylvania felt for Hillary and didn't manufacture enough fake votes in those states to counter Trump's message (unlike in California where they continually overdo it.)
You bet they will not make that mistake next time - and the midterms proved they've got the fraud engines humming already.