More Americans are now “unsure” about the deal.
President Obama is urging supporters to back the Iran nuclear deal and counter a well-funded lobbying effort already mobilized against it. The administration so far lacks sufficient support to sustain a presidential veto if Congress votes to reject it. 
A new YouGov poll on the Iran nuclear deal finds the president may have good reason to be concerned, as public support has softened significantly over the past ten days. Just 36% of the public say they back the deal in the latest poll, down from 51% in YouGov’s previous survey. However, opposition has not increased so dramatically. 38% now oppose the deal, up from 33% in the previous poll. Meanwhile the number who are unsure how they feel about the deal has increased from 16% to 26%.
Much of the shift can be accounted for by a large drop in support among political independents, with whom support has fallen by 25%. As with the numbers for the general public, however, opposition to the deal has increased only slightly, from 33% to 37% while the ranks of those unsure how they feel has grown by 21 points.
But the president may be wise to caution that opponents of the deal have been galvanized to a greater extent than those favorable to it. The number who “strongly” oppose the deal (24%) now more than double those who “strongly” support it (11%). This includes about half (48%) of self-identified Republicans who strongly oppose the agreement, which may be evidence that the escalating rhetoric and unified opposition of Republican leaders in Congress and among presidential hopefuls may be having an effect.