I went with never. I think if it does happen it's more likely to be between India and Pakistan. As mentioned by someone else, they seem to be in a cooling down period currently. Hopefully they will play nice with each other.
I think it's more likely that it will be something set off in the back of a truck or car, by some radical (pick a flavor). Now, if that happens to be a car or truck setting in Downtown Jerusalem, then I suspect that at least one major city in the Middle East will suffer retaliation on a grand scale. I hope it never comes to that, but I fear it's just a matter of time. And I think we (the US) are almost as likely a target as Israel.
I don't think any sane nation would try a full frontal nuclear attack on the US. Having served as a "Cold Warrior" (11 FBM Submarine Deterrent patrols, 72 days each on average, under the water), and knowing what our abilities were when I got out, and having seen the next generation of gadgets that were going on the Trident II Fire Control System/Ohio class Submarines, I have no doubt that we could rain down a torrent of nuclear warheads that no defensive shield could withstand, and that could be done if every man/woman/child on land in the US was dead, and every plane/satellite shot down. It would be suicide on a national level to even try it. Of course if
Nuclear Winter is a valid theory, it might be suicide on a global level
Even using air burst detonation for a "cleaner" explosion (not as much surface matter is thrown up to be contaminated and blown about as with a ground burst) there would likely still be more than enough radiation spread around to make things pretty ugly. Would it be an
Omaga Man scenario? Probably not, but I think those areas most affected by the radiation cloud would be devastated, and that the results would make Chernobyl look minor in comparison.