Somebody: The war in Afghanistan is completely off the radar of most Americans today. According to a NY Times/CBS poll only 3% of Americans rated it as the most important issue. Americans may not be enthusiastically supportive of Obama's counter-insurgency in Afghanistan and Pakistan, but they don't especially care either. This is in sharp contrast to the last mid-term elections in 2006, when the Iraq War was at it's peak.
Honestly, the Afghan War is a loser as an issue. Even the left can't get excited about supporting a Taliban-led insurgency.
Moreover, Obama has largely kept his commitment to withdraw combat troops from Iraq. His reward for winding down the war? Well, there is none. Even folks on the left can't admit that he's ended the Iraq War.