Same thing for gas. Obama did nothing to lower gas prices. But imagine if for whatever reason (say a hurricane came through and knocked out US refining capacity two months before the election), he would've got the blame for high gas prices. And not just Obama, the same situation kind of happened to Bush when Katrina knocked oil infrastructure offline.
It's the same thing with factory jobs. The US produces more than it ever has (at least the last time I checked), but many of those jobs were automated away.
http://www.marketwatch.com/story/us-manufacturing-dead-outpu...