Look at the Soviet Union at the end of the 80s, look at Cambodia just a few years ago. When a dictatorship thaws and loosens up it doesn't just wipe the slate clean (that would require bloody revolution). It's a bunch of small things that signal a shift.
As for Iran, I'm of the opinion that there is a core of pragmatic heads within the leadership who will marginalize the crazy-nuke-Israel-no-matter-anything-else sort and go with the MAD doctrine everyone else follows... Which is probably just as bad a scenario in Netan's opinion anyways...
I put these two together because they kind of hand waive the completely unambiguous threats that still sometimes come out of Iran...as long as some vocal power in the Iranian government with any sort of authority keeps saying "Death to Israel", it's hard for the other half of people not willing to be open minded to see them as anything other than a threat. And, I mean, that's the threat of threats. It's not like NKs threats, they're expressing an underlying political philosophy that is "Fuck Israel." You can thaw and marginalize all you want, but for a county like Israel, and for people who do want to hang Islam out to dry, statements like that are all the ammunition they'll ever need to keep this thing going. Although Khomeini isn't as vocal as he used to be, I think even just last year he said the same overall goal was the complete elimination of Israel. He and others like him don't reset the cooperation clock when they do that...but they do prevent it from ever moving beyond a certain point.
So that level of vitriol has to be dealt with, and it will probably taken a couple generations for it to work itself out of the political culture of Iran, to the point none of these people hold power anymore and marginalized. Assuming it, Israel or half the world isn't a smoking crater that point.
FTFY
Any sort of US military engagement to protect Israel from Iran would pretty much be perceived as us achieving what we want as well (other than protecting Israel.) It's hard to say you don't have a vested interest in an outcome when you're attacking an entire country. And depending on who wins the election, the desire to attack Iran might go from right-wing crackpot saber rattling to US Foreign Policy.