Not just because Iran would perforce be pushed deeper into the embrace of the PRC by a renewal of Western hostility.
The PRC has always been recognized as the key to effective Iran sanctions. The Obama adminstration invested enormous efforts in finessing the China factor as it pushed for UN sanctions against Iran in 2010.
And it yielded results. So, like the title says, If You Like the Iran Nuclear Deal, Thank China.
The historical record implies that the Obama administration didn't quite push the Chinese dragon to its knees; it looks like some serious tummy-tickling of the PRC panda was also involved.
A review of the sanctions campaign against Iran at the UN in 2010 offers an indication of what was and what might have been: a few months at the beginning of the Obama administration when the US saw engaging and haggling with China on Iran as a worthwhile national objective.
Now, the Chinese key to effective Iran sanctions is becoming is becoming less and less accessible.
Because China, unlike the EU, has a suite of countermeasures to US national sanctions coercion in the financial realm that, though nascent, could be made more effective and robust by implementing them in the relatively friendly battlespace of a sanctions war that most US allies are demonstrably unwilling to support.
Count the development of a parallel PRC international financial infrastructure as collateral damage of the US China rollback policy since 2009 and, more recently designating the PRC as an adversary of the "rules based international order" and not a legitimate great power interlocutor.