Alan, I think Mark meant that Iran would use chemical weapons against US ground troops; but his post was not clear on that. And the Iranians now first-hand the devastating results of that from the Iraq-Iran war. But I think the Iranians will, for that same reason, be very reluctant to use them.
Saudi FM: We hope Iran uses sanction relief for development, not nefarious activities (Reuters)
from the article: Will Bush make Iran the only superpower?