Are Americans stupid? No, they are not. But as someone who has watched this close up for nearly 50 years, it's my opinion that that by and large, and especially with regard to the younger generation, Americans, today, are more ignorant in many respects than they were decades ago.
There are two primary reasons for this.
One deals with the continued decline of the American educational system which began with the recognition that American education was failing as compared to achievement levels of other nations. And so, the federal government started leveraging money with secondary educational achievement, and the result of that was an intentional dumbing down of the curriculum so as to keep the money coming in. That led to less educated students. Those who went on to college required massive remedial education to the point that colleges, too, began dumbing down curriculum. Bottom line: today's high school graduates and today's college graduates know less than their peers of a decade go, and even less than their peers of several decades ago, etc. Today, the typical high school diploma which states that the student has achieved a secondary education and is capable in math, science, english and social studies, is largely a fraud.
The other reason is the social engineering that began with the Great Society and has continued to what we have now, an entitlement society where there's no incentive to learn so as to better your position financially, because, government will take care of you regardless.
It isn't just politics, or the world around them. Today's younger generation, by and large, is largely ignorant - relatively speaking - about practically anything outside the entertainment world. And the dumbing down of America continues.