Raising Iran’s LEU to higher enrichment levels is a step backwards. Two-thirds of the work to get 90% enriched uranium, the most efficient weapons grade, is accomplished when U235 isotope levels in natural uranium are enriched to Iran’s current level of approximately 3%-5%. Further enrichment of Iran’s LEU to 19.75% is a significant step in the wrong direction. This is barely under the 20% definition of weapons-grade, highly enriched uranium (HEU). Ironically, Resolution 1887, adopted while Mr. Obama presided over the Security Council last week, calls for converting HEU-based reactors like Iran’s to LEU fuel precisely to lower such proliferation risks. We should be converting the Tehran reactor, not refueling it at 19.75% enrichment.

After Geneva, the administration misleadingly stated that once fashioned into fuel rods, the uranium involved could not be enriched further. This is flatly untrue. The 19.75% enriched uranium could be reconverted into uranium hexafluoride gas and quickly enriched to 90%. Iran could also “burn” its uranium fuel (including the Russian LEU available for the Bushehr reactor) and then chemically extract plutonium from the spent fuel to produce nuclear weapons.

The more sophisticated Iran’s nuclear skills become, the more paths it has to manufacture nuclear weapons. The research-reactor bait-and-switch demonstrates convincingly why it cannot be trusted with fissile material under any peaceful guise. Proceeding otherwise would be winking at two decades of Iranian deception, which, unfortunately, Mr. Obama seems perfectly prepared to do.