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Last week, we wrote on this page that given the Obama administration’s lack of leadership on Iran in this “period of consequences,” Congress should step in to fill the void. As our editorial went to press, a bipartisan group of 44 senators began to do just that. In a letter organized by Senators Robert Menendez and Roy Blunt, the group outlined a series of steps Iran would have needed to take at the June 18-19 Moscow talks to justify further negotiations. These included shutting its previously covert enrichment facility near Qom, freezing enrichment above 5 percent, and shipping its stockpile of uranium enriched above that point out of the country.

The letter noted, “Absent these steps, we must conclude that Tehran is using the talks as a cover to buy time...