How much does smoking affect strength gains

I've always felt like i'm not getting any stronger in the gym, even after a couple years of gym going. I would like to quit smoking for all the obvious reasons, I just haven't been able to yet. Would this explain why I seem to be getting nowhere, despite following workout plans that are supposed to work. I eat pretty well, I keep my diet to lean proteins, low fat and some carbs. Is my one stupid habit what's holding me back?