Wendy Sherman actually said...

the problem--of course the Iranians know we will pass sanctions if they do not agree.

We would not have agreed to an extension if we didn't believe we had made tangible progress and we did not see a path to a...

Sanctions did not stop Iran's nuclear program. Sanctions brought Iran to the negotiating table.

I do believe that the Iranians want relief from sanctions and that is why they are at the table.