Granted Senator Obama "quit" smoking about a year ago (he admits falling off the wagon now and again), but this is still a very current health issue for him since he did smoke cigarettes for the majority of his life.
I mean, the amount of fatty deposits in a carotid artery doesn't just go away when you quit smoking. It's there and poses a health risk for the rest of your life.
And the risk of a stroke remains way higher than normal for up to 20 years after you quit smoking. (On top of this, African-Americans have a higher risk of stroke than Caucasians.)
So do you choose a presidential candidate even though he's at a very high risk of disease/death? Does it matter that for decades he has been addicted to a drug?
How would you feel seeing the US President attached to an oxygen tank?