Opinions have moved from a 2-to-1 margin in support in March (59-31 support-oppose) before the final agreement was negotiated between Iran, the United States and five other world powers. Support was lower still, 45 percent, in a separate support question which included fewer details about the agreement.

The decline in support has been driven by Republicans, who moved from 47 percent support in March to 30 percent now. Support has slipped among independents, but by a smaller degree. Two-thirds of Democrats currently support the deal, as do half of independents…

A variety of public polls have shown declining support for the deal, falling as low as 21 percent approval in a Pew Research Center poll earlier this month (with 49 percent disapproving). Much of the variation in support or opposition between different polls can be traced to how the questions have been asked. Questions that include more details about the deal have generally found more support, while questions with fewer details find less support.