A US intelligence report, released not long ago, reversed the opinion of the last assessment made public. The newer one said that Iran ceased its
efforts toward nuclear weapons production.
However, it does not say that the opinion is based on any further evidence than the previous report, which presented the opposite conclusion.
Presently, some commentators suspect the conclusions in the new report now reflect political considerations, rather than what is really likely, based
on the evidence available.
However, it could be just as valid to argue the other way, that the previous opinion reflected political bias, and the newer report is more
Without ability to examine the sources (which would include non-public sources), it's hard to tell. It is partly, whom do you trust?
There is also the consideration--if you over-estimate Iran and are cautious, you don't lose anything (provided you don't provoke a war). But, if
you under-estimate Iran, and they are further than you think, the consequences could be grave indeed.