All President Obama has to do is announce the immediate pull out of all troops from Iraq and Afghanistan. Not only will it energize the Democratic base, it will provide a major talking point when Mitt Romney and other Republicans denounce it.
President Obama can then simply accuse Mitt Romney and other prominent Republicans of being chicken hawks, by pointing out how easily they are willing to sacrifice the lives of so many brave young Americans, in far off lands, while they and their families sit in luxury in their mansions. [Something the president, in good conscience, isn't willing to do any more!]
Then President Obama can go on to point how Mitt Romney and others, by evading taxes for the past 10 years, showed their lack of willingness to even help fund those wars, but instead called for even lower taxes, and to pay for those wars through even greater cuts to social security and medicare, two programs designed to help the most vulnerable members of society.
It's a simple strategy, that will be hailed by progressives and many others alike, will put Mitt Romney and Republicans on the defensive, and without question sway the election in the favor of Obama.