It may be a problem with conservative voters, although from what I can tell, it really wouldn't be that difficult for liberals and Democrats to bring a large segment of the working class over to the left - if they really tried. The trouble is, they're not trying hard enough. The Democrats stopped being the party of the working man and became the party of the non-working man. If they'd focus more on improving the lives of workers in this country, they might actually make some progress. Instead, they chose identity politics which doesn't help workers one iota.
As a result, a lot of these "conservative voters," dumb or not, feel they're going to get screwed either way, so they'll vote based on the agenda and choice that is presented to them by both parties.
The Democrats are no longer the party of FDR, Truman, or even JFK or LBJ anymore. They've actually become far more conservative themselves. Support for labor unions has all but dried up. That happened when Clinton did a bait-and-switch and became an ardent supporter of NAFTA, which alienated a lot of voters in what is now known as the Rust Belt.
A lot of it also has to do with attitude. Quite frankly, a lot of liberals have a certain chip-on-their-shoulder arrogance and condescension in that they think they know what's best for everyone. They need to drop that attitude. The Ivy League, urban sophisticates who think they're soooooo clever and enlightened aren't as smart as they think they are. They need to stop these transparently supercilious games they play and start showing some real empathy for the daily struggles that a lot of people go through. I see this quite often in many debates on politics, even here on RF. This arrogant pretense has to stop, along with the propensity to denigrate and put down others just so they can feel superior and more "enlightened." Some people can see through their faux compassion and phony smiles and see the underlying malice and disdain they have for the lower classes. They may not be as dumb as you think they are.
If what you say is true, that conservatives have gotten dumber over the past 40-50 years, then the same might also be said of liberals. The liberals I remember in my youth used to see things in terms of cause and effect, in not attacking symptoms but getting to the real root of whatever problems we were facing. They're not doing that anymore. Liberals only seem interested in appearances, superficiality, and surface level political correctness that they don't even bother to scratch the surface and try to see what's underneath. Maybe because they're afraid of what they might find.
I've seen these people, living in the lap of luxury, while leisurely lounging around at Starbucks drinking lattes and acting as if they have all the answers. They think they're so cool, hip, and sophisticated while smugly looking down on all the "dummies" and "hicks" who voted for Trump and support conservative candidates. That's how they come across, and yet, they don't spend enough time on introspection and truly looking inside themselves to realize it. They spend too much time judging others that they've lost sight of just how truly out of touch they've become.
Eventually, I see the left and right going further to the extremes. The left's best hope is to try to unite the lower classes by abandoning identity politics and lining up with each solely on the basis of economic class, which would ideally lead to the overthrow of the wealthy elite and bring about total class equality. That's what I would support. But the pro-capitalist neo-liberals who enjoy living in the lap of luxury will never go for that, so they're the greatest obstacle to overcome before anyone can even think of challenging the pro-capitalist neo-conservatives who are backed by the lower classes of middle America.
The lower-class conservatives of middle America also embrace their own form of identity politics which many liberals deride as hateful, homophobic, racist, xenophobic, sexist, etc. who share many of the qualities commonly associated with Trump. They don't seem to care so much about class or social inequities as long as they still feel a useful and integral part of America and get what they feel is "theirs." They really don't care if gay couples get a wedding cake, and they care even less about the plight of immigrants who seek a better life in America. They don't care about feminists breaking through the glass ceiling, and they don't really believe that black lives matter.
These people are full of anger, bitterness, and hatred, and they don't care who they have to (literally) roll over to get a better life for themselves and their own. They're also heavily armed and preparing for armageddon. They may or may not believe in trickle down economics, but they ostensibly believe that by getting rid of certain segments of the population, their own lives will get better. I've run into quite a few of them here in AZ, and I've also known them in my extended family. They're not really that dumb, as they have a lot of practical skills and are very mechanically-minded, even if they can't spell or write very well. They know how to build stuff, they can fix machinery, they can dig tunnels underneath their houses, they know weapons, how to hunt, how to grow food - and many of them feel as if God is on their side. They are immune to judgmental liberals and their tactics of ridicule, and the more that liberals mock them, the more entrenched they become and feel that they're right, down to the very core of their being. Liberals who insulate themselves in their "safe spaces" and gated communities truly have no idea what's going on.
It's easy for you and others to sit there in judgment, as if you think you're smarter than everyone else, but I am truly disheartened and weep for America's future. We are going down a road which may have no turns.