Very few Americans understand Evolution, including the ones who believe in it. Many have a partial understanding of it at best, and they couldn't tell you much about why Biologists are certain its true, though they might be able to mumble something about "fossil evidence."
This is my impression having spent decades discussing the subject with many people. I often hear so-called Evolutionists saying incorrect things about the subject — even while they're arguing with Creationists. I have stopped being surprised at hearing errors from both Evolution apologists and Evolution skeptics.
Whose fault is this? The Education System. Even in places where the subject is openly taught, it's often taught poorly. Either the teacher doesn't understand it, or he does but his teaching methods are shoddy. He winds up boring his students, and they don't recall what they've learned.
Don't believe me? Okay, find out for yourself: first, make sure you really understand the subject. I recommend this book: Amazon.com: Evolution for Everyone: How Darwin's Theory Can Change the Way We Think About Our Lives (9780385340922): David Sloan Wilson: Books Or, at the very least, fully read some wikipedia articles.
Then ask 20 friends (who believe in Evolution) to explain Evolution to you. Ask them to explain in detail, and ask them to explain why they believe whatever they're saying is true.
Can they answer these questions?
1. What are the specific mechanisms that allow offspring to differ from parents, in both sexual and asexual-reproducing species?
2. What are the requirements a system needs in order include Natural Selection?
3. What is the relationship between chimpanzees and humans?
4. How can features like the eye evolve independently multiple times?
5. Does it make sense to say that one organism is "more evolved" than another?
6. How long did it take for humans to evolve to their present state?
7. Can an organism exhibit a trait that isn't evident in its parents without mutation having occurred? How?
8. What is Kin Selection? What is Group Selection? What are the pro and con arguments for them?
9. Does Evolution have a purpose? Does it make sense to say that a certain trait evolved for a purpose?
10. Can a trait survive in a population, even if that trait doesn't give its hosts a reproductive or survival advantage? If so, how?
11. What is Punctuated Equilibrium and what are the arguments for and against it?
12. What do scientists mean by the word "theory"?
13. What evidence has convinced Biologists that Evolution is true?
What irks me is that if Evolutionists won the battle over what's taught in schools — if all schools agreed to teach Evolution and not Creationism — most people who believe in Evolution would pat themselves on the back and move on to another battle. This is because they are more concerned with the battle as a symbol than whether or not children are actually learning anything.
Yes, we can blame the Creationists. They are an easy target. But don't think if they all vanished tomorrow, we'd have a population that understood the subject. They might believe in it in a dogmatic way. In which case it's magical thinking that just happens to be true.