They probably won’t set off a nuke in Manhattan, or “lose” one of their nukes to their terrorist subsidiaries, at least unless they’ve got a really surefire way to get away with it.
But observe that they are already backing at least part of the “insurgency” bedeviling Iraq. If they go hog-wild, we can always muster support for an invasion – for now – so there’s limits to what they can do there.
But with a nuke, they’ve suddenly invasion-proofed themselves. Like the Pakistanis, the Chinese, and the Russians, they’ll either get nuked or scolded and/or embargoed, but almost certainly nothing in between.
All of a sudden, the limits to their insurgency-backing activities in Iraq are gone. We’re going to enter a nuclear exchange because they’re vigorously backing insurgents? Not bloody likely.
So what we end up with is a proxy war against another nuclear armed power. We don’t have the option to take the fight to the backers no matter how much they escalate the situation, because they’ve got nukes. So we’re stuck blasting away at their agents (who quickly get replaced by the backer) and taking significant numbers of casualties in return for years on end, making life awfully rough for the locals in the meantime, until one side finally runs out of patience and throws in the towel. If it’s us that throws in the towel, then life gets really rough for the locals and our reputation goes in the toilet.
That sounds awfully familiar. Didn’t John Kerry make a passing reference to the time he was in that situation a few decades back? As I recall, it didn’t turn out too well last time around…