I've been to Nagasaki. Took my son on a side trip when we went to Japan with his middle school Japanese class. The news about Obama reminds me how we felt seeing melted hand bones in museum case. It's an incredibly emotional experience, I don't think you can imagine unless you've actually been there. It should be just an historical site, like a gazillion other historical sites. But it isn't.
I heard a Hiroshima survivor talk on NPR today. (You can find the audio and transcript here). It's harrowing hearing the experience she went through, but it's good to be occasionally reminded of the nuclear threat that's still an issue today.
A very strange details is that back in 2009, Obama tried to get Japan's approval for him to publicly apologize on behalf of the US for the bombings, but the Japanese vetoed the idea. The Japanese politicians had some strange ideas to justify this refusal.
They probably felt that it would cause a political crisis and risk straining relations. Still, it must have been harrowing to go through that. :[ The worst damage isn't from the initial blast, but the radiation that comes afterward. And you might not know you've been affected until decades after it happened.