I think you have the basis for a good thesis statement here, but it might need just a little tweaking. It sounds to me as if I've come in in the middle of a conversation. When you say "this growing trend" it sounds as if you are referring to something you have previously been discussing. If this is not the first sentence of your essay, then it may be all right; I'd have to see it in context. If you planned for this to be the first sentence, I'd make it the second, and have a first sentence something like "Over the past three decades, conservatism, in politics and social mores, has been gaining strength once again across the U.S."
I hope this helps!