CA-11 is quite a different beast than Oklahoma and Inhofe is probably just trying to stir things and maybe boost fundraising. Or maybe he's just trying to show paranoid behavior; wouldn't be the first time.
It would take a pretty credible challenger to beat him and I haven't seen an interest in Gov. Henry or the younger Boren in testing out Inhofe.
The secret to Inhofe's success is strong performance in Tulsa, where he was mayor. A good Dem would have to beat up against those margins somewhat and perform well in the rural east to have give himself a shot.