Large majorities of Democrats and independents, and even half of Republicans, believe the president of the United States should meet with the leaders of countries that are considered enemies of the United States. Overall, 67% of Americans say this kind of diplomacy is a good idea....
About 6 in 10 Americans (59%) think it would be a good idea for the president of the United States to meet with the president of Iran. This includes about half of Republicans, a majority of independents, and most Democrats.
This suggests that McCain has framed the opening of the general election, in part, on a serious losing issue. Although I wonder how much those numbers shift when you start reminding people, as McCain is, of specific things the president of Iran has said and done.