Sorry -- Zero Credibility
The US openly meddles in other country's affairs, directly through the State Department and indirectly through a plethora of NGOs. These agencies also don't seem to mind propaganda originating from outside provided its coming from 'friendly' countries with the appropriate messages (usually ultra-right wing). The only problem they have is with sites from countries that might present alternative views of both internal and external affairs. Its just censorship masquerading as legitimate law enforcement activity.
I've been quite fortunate in that living in California nobody in DC has thought it worth spending money on campaigning here -- there's been a couple of nominal visits but by and large we've been spared the deluge of crap that accompanies elections. (Its been reserved for the Propositions instead. These have once again demonstrated that we have The Best Democracy Money Can Buy.)
The most potent form of propaganda from places like Iran is the home videos you get from travellers on youTube, "What I did on my pilgrimage", that sort of thing. Iran and especially Tehran seems to be getting by just fine despite the restrictive sanctions regime. We're fed a carefully curated news diet about life in these places because they're not places any of us can visit so seeing the place shows just how badly we're being manipulated by our own governments.