WASHINGTON – It will be the DC equivalent of the showdown at the OK Corral. Stepping into the summer haze on Capitol Hill, the American Israeli Public Affairs Committee and its allies are set to face off against the ultimate power broker – 1600 Pennsylvania Avenue – backed up by a cadre of its allied groups.

The lobbying showdown, over a Congressional vote on the nuclear deal with Iran, represents a rare moment for AIPAC, with the avowedly bipartisan organization publicly splitting with the sitting administration over a major foreign policy initiative.