Pew Research poll, acceptance* of the Theory of Evolution in the US has remained steady overall for the last four years. However, it has declined among Republicans, from 54% to 43%.
Now, a 60% acceptance rate for a fact of nature is nothing to brag about - it shows that epic levels of denialism and scientific illiteracy abound in our country. That being said, I am encouraged by one thing: If the overall level holds steady, but denialism increased among the GOP, that means that the rest of us are getting smarter. Finally.
*I say "acceptance," not "belief," because belief implies that evolution is an article of faith. It isn't. Instead, it is by far the best explanation for a staggeringly, definitively enormous collection of natural evidence. One "believes" in evolution in pretty much the same way one would "believe" in gravity.