Hillary was probably the worse:

I won the places that represent two-thirds of America's gross domestic product... So I won the places that are optimistic, diverse, dynamic, moving forward. And his whole campaign, ‘Make America Great Again’, was looking backwards,

Obama:

Referring to working-class voters in old industrial towns decimated by job losses, the presidential hopeful said: "They get bitter, they cling to guns or religion or antipathy to people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations."

John Kerry:

You know, education, if you make the most of it, you study hard, you do your homework and you make an effort to be smart, you can do well. If you don’t, you get stuck in Iraq

These are slip ups, if you search for coded ways they describe their opponents, you can find a lot more "low information" and "uneducated" examples.

Remember Joe the plumber? He was a reaction to republican voters feeling unrepresented as blue collar workers.

This kind of class contempt absolutely isn’t unique to Democrats, but their obsession with courting higher educated voters has branded their contempt for those who aren't.