What we don’t know is if a successful Israeli attack on Iran’s nuclear facilities would discredit the regime to the point that it would be forced out of power or if such an attack would be used to discredit the opposition, causing Iranians to close ranks behind their extremist leaders.
Generally, when bombs fall on people, they get mad at the people doing the bombing. It’s a simple enough lesson, but one that many, in their unconsidered haste to bring about the regime’s downfall, miss quite entirely. The second of Johnson’s possibilities, or a version of it at least, seems much more likely to result from a missile attack; this would only enhance the government’s hardline posture, and give needless credibility to its attempts to focus attention on outside “enemies.”
If Israeli bombing discredits the Iranian regime, it will be approximately the first time in the history of the world that such a thing has happened. The closest case would appear to be that of Slobodan Milosevic after the Kosovo War, but a much more compelling argument can be made that Milosevic fell because he gave up, rather than because he fought.