Response:

Actually, diplomacy with Iran has not been tried, at least not by the United States.  It is sanctions that have been tried and failed.  For five years until nearly the end of its term, the Bush Administration refused to talk to Iran at all about nuclear issues -- because Iran would not comply with U.S. demands that it first suspend all enrichment. This strategy merely squandered time: while the U.S. sat silent, Iran continued to enrich.

It is true that the Europeans talked to Iran, and they didn’t make much progress. But this is hardly surprising.   Without the United States – the world’s sole superpower and Iran’s chief nemesis – at the table, why should Iran give its best offer to Britain, France and Germany? They would just pocket Iran’s concession, which would become the starting point for later talks with the United States. more

Real diplomacy on this issue has not been tried. What has been tried is threats and sanctions, and everyone agrees they have failed to achieve our objectives.  They may well have set us back by galvanizing Iranian resistance. More of the same is not going to produce different results, and trying for "crippling sanctions" will only make things worse.