- Iran signed an NPT [a non-proliferation treaty] long ago (see this), albeit under the Shah.
- Iran breaches NPT
- US and the west try to negotiate something to be able to enforce the original NPT.
- US and the west agree to weakened conditions of original NPT.
- and the US and the West believe Iran will honour the new agreement.
Compliance failure is hard wired into the agreement, according to this account: