If this were 2008, yeah, Hillary could get 40% in Oklahoma. However, her ceiling now is 36-37%, I believe. The reason it has gone down is simply clear: Barack H. Obama. If Hillary hadn't become the Secretary of State and appeared to have shifted drastically to the left then she might have done well, but Obama did her in here, I believe. If Obama were to run again in 2016, he would be in jeopardy of only getting in the 20's in Oklahoma. This state is anti-Obama to the core.
No way Obama could go lower given his having reached the bottom threshold of the Democratic vote in 2012. Who in Oklahoma who is going to vote Republican didn't in 2012.