> They are trying to build a nuclear weapon
So far everyone who has tried to prove this claim - including the CIA and Mossad - has come up short.
No, nobody seriously thinks that. The CIA isn't even trying to prove it.
Unfortunately, everyone is reading a bunch of journalists who lack even the slightest ability to parse nuance. Iran is trying to build a nuclear breakout capability.
Every serious report that has ever been issued says exactly the same thing: No evidence of a nuclear weapons program, undeniably overwhelming evidence of Iran attempting to gain breakout capability.
Yes, there is evidence of weapons-related development (delivery systems, etc.). Yes, they have a growing enrichment program that is geared towards weaponization. Yes, they want to be able to build a weapon. No, there is no evidence that they have built a weapon or plan to immediately do so.
Breakout capability is still scary, though. It means they can have all the pieces in place to produce a weapon before anyone can mobilize sufficient resources to stop them. Given the regime's behavior, you should be able to understand why that concerns the rest of the region.
I've posted this with complete links and lots of details, but I'm not bothering to do it anymore.