While I would agree that not everyone who voted for Trump is dumb or poorly-educated, it is also true, in an objective sense, to state the simple fact that Trump's base does tend to consist of those without college degrees. A college degree doesn't equate to intelligence, god knows, but as I said in another post a big part of the Trump phenomenon is a deep resentment and grievance towards the college-educated professional classes (especially upper-middle-class white professionals) by mostly working-class, non-college educated, and often rural or exurban whites.
And if by "rube" you mean someone who is easily conned and gullible and who has fallen for Trump the con man, then I would also certainly argue that is largely true, whether you're talking about college-educated, non-college educated, or minority voters who voted for Trump. And for proof just look at all of the interviews with Trump supporters since 2016 - the man they consistently describe voting for simply doesn't exist in reality; he's a figment mostly of their imaginations.
As for this hurting Democratic politicians, I'm not sure what they can do to win over most of these people anymore. I'm sure that you and others will say that Democrats need to "stop looking down" on Trump supporters, but the problem with that is that no matter what Democrats do Fox News and Newsmax and OAN and right-wing talk radio will continue keeping them in a state of resentment no matter what. I do agree that Democrats need to focus on winning back minority voters, but I'm not sure what can be done to win back the vast majority of Trumpers. They simply love the guy and do follow him blindly, because they're in a cult, plain and simple.