As Iran and six world powers meet this week in Vienna to begin drafting language to resolve their nuclear standoff, negotiators say they are finally confronting a crucial sticking point to a permanent agreement — the size and shape of the nuclear fuel production capability that Iran will be permitted to retain. It is a subject that, at least in public, the Obama administration steps around, acutely aware that Israel and members of Congress who are highly suspicious of the negotiations will say that Iran must be kept years from being able to develop a weapon, and that opponents of the deal in Tehran will argue that no restraints at all should be imposed. Both the Iranians and the Western powers have said their talks so far have been productive, with little of the drama, the ultimatums and the entrenched positions that have marked previous efforts. But […]