If you want to know why US policy, from Bush to Obama, is cataclysmically wrong on pushing the European Union to make Turkey a member, you couldn't do better than by reading this excellent book, A Bridge Too Far, by Philip Claeys and Koen Dillen. The authors, members of the European Parliament from the Vlaams Belang party in Belgium, make the compelling historical, religious, cultural, and economic argument against Turkish membership in clear and logical prose.
Hint: It all has something to do with the fact that Turkey is a part of Islamic civilization, not Western civilization. If it joins the EU, it becomes the largest EU state, suddenly adding 70-plus million Muslims--presto--to "Europe." In other words, Creeping Sharia becomes Leaping Sharia.