That's actually an important point. I wonder what Britain, France and Germany will do. We are signatories of a treaty with Iran that Trump abandoned.
Will we let the US be seen to be alone?
We may feel we have to give the appearance of being supportive rather than leave the US out on a limb. But it would be asking a lot to have us join a war because the US president doesn't have a strategy, and appears to be macho-signalling for electoral purposes. It isn't any country's job to help Trump win the next election.