Why not cap Iran's enrichment and in return ease some of the sanctions? Certainly, election-year politics and hawkish congressional pressure ensures that the US administration (which leads the P5+1 in these talks) cannot consider easing sanctions no matter what Iran does with its nuclear program. President Obama would be cast as “weak” if any of the sanctions were lifted before the elections. Oddly, a successful diplomatic resolution of the Iran nuclear issue would be spun as a failure.
Unless the P5+1 nations can specify exactly what Iran would need to do in order to begin to ease the sanctions, further talks – planned for next month in Moscow – seem like a waste of everyone's time.
The sanctions appear to be a one-way street: They are easy to enact as punishment, but evidently cannot be removed to reward positive Iranian behavior. The net result is that the Iranian people suffer, the Iranian regime keeps stockpiling more and more enriched uranium, and the US congressional hawks can feel smug in the false knowledge that continued sanctions will magically lead to regime change in Tehran.
In fact, a careful reading of the legislative text of the sanctions shows that the sanctions have very little to do with Iran's nuclear program and everything to do with regime change. For instance, the US sanctions can only be lifted after the president certifies to Congress: