We only have 11,000 troops there compared to the 100+ thousand in Iraq. The distraction in Iraq was the death of the Afghan campaign.
The US military has over a million soldiers (I think 1,400,000 was the number). The reason for which there are only 11,000 troops in Afghanistan is because the army doesn't think more are necessary. The army can easily dump 500,000 troops in Afghanistan (while also dealing with Iraq), but that would A) provide more targets of opportunity for terrorists, and B) congest the process of going after them. A larger military force does not necessarily mean a more efficient one.
The war in Iraq did not in any way hinder the war in Afghanistan. That's just rhetoric that certain politicians are throwing around for their own personal gain, but there are no facts behind it.