I think you underestimate the number of people who protest voted by refusing to vote at all, which is neither an actual protest vote nor the same type of problem. Not that I think it would have been a guaranteed tipping point, but it sure would have made things a bit closer. Compound that with one of the (designed) effects of the electoral college (devaluing voter turnout in high-population states), and you widen that gap much more.

"America will have the most lethal military" and other signalings in favor of status quo imperialism sure did kill any interest for many left wingers to vote, and anecdotally I know many of my left-proclaiming peers took that as reason to forego the polls altogether.