At a San Francisco fundraising event on April 11th, Obama said about small town people in Pennsylvania and the midwest:
they get bitter, they cling to guns or religion or antipathy towards people who aren't like them or anti-immigrant sentiment or anti-trade sentiment as a way to explain their frustrations.
The comments make more sense when taken in their context, but many Americans are upset about them. Here is Hillary Clinton's and John McCain's response:
And finally, here is Obama's response: