The letter reads in part:
"Our diplomatic goal must be to reach a negotiated settlement in which Iran agrees to verifiably dismantle its nuclear weapons program. For this outcome to be realized, Iran must face intensifying pressure. This means the full implementation of current sanctions available to your administration, and further legislative steps to close loopholes and broaden our sanction’s reach."What that means is "we demand you put even more sanctions on the Iranian people to punish them for having a government with whom we disagree." And the justification for demanding additional sanctions is a nuclear weapons program that even the US intelligence community does not believe exists.
Instead of finding a way to deal with the Iranian government in a straightforward and honest manner, Congress continues in its counter-productive, heavy-handed interventionism.