I was born in 1955, and in my lifetime, the pundits assured us that the American people would never elect John Kennedy, because he was a Catholic. After a devastating loss in the California governors race against Pat Brown, we were all told that Richard Nixon's political career was over. He was no longer electable. Jimmy Carter, a one term Governor from Georgia, was a political joke. Another southern Governor, Bill Clinton, was a womanizer, somewhat shady, and after a disastrous keynote address at the previous Democratic Convention, one of the seven dwarfs, and was dog meat against a popular sitting President. And let's not forget how we were all assured that America wasn't ready for a black President, and that Barack Obama was nothing but a speed bump on the road to a John McCain victory.
I'm not predicting that Donald Trump or Bernie Sanders will be the next President. Quite frankly, my feeling is that Donnie will probably go third party and guarantee a Democratic victory. As for Bernie, I think he's got a shot in a week field, (And yes, I do include Hilary in that.) though it's unlikely. The point is, the American electorate doesn't always follow the advice of the talking class.