President Obama job approval rating has been static for the past three months. Since mid-August, net job approval for President Obama has hovered in a tight, 5-8% net approval range. This range is very similar to the amount by which he won the 2008 election (7.27%), strongly suggesting that the national political environment has simply returned to its pre-election coalitions. President Obama's supporters are now the same group of people who voted for him last year, while his opponents are those who voted for someone else.
Since he is now relying on his pre-election coalition to maintain his overall support, any decision to further escalate American troop presence in Afghanistan is dangerous for President Obama. This is not only because a narrow majority opposes troop escalation in Afghanistan, but because the majority of Americans who oppose the troop escalation are members of President Obama's coalition (aka, mainly self-identified Democrats).
By a 2-1 margin, self-identified approve of President Obama's handling of Afghanistan, even though twice as many Democrats favor decreasing troop levels there as favor increasing troop levels.
Already, a 27% disapproval for President Obama among Democrats for his handling of Afghanistan is far above his overall job disapproval among Democrats, which only stands at 12.3%. If an additional 15% of national Democrats were to start disapproving of President Obama's overall performance, then his overall job approval rating would slide to around a net negative of 4-5%. Such a negative approval rating would seriously endanger the rest of his legislative agenda, from health care to climate change to financial regulations.
President Obama is not going to win back any significant number of Republicans, who overwhelmingly disapprove of his handling of Afghanistan despite approving of his policies there. It is also unlikely that he will win back a significant number of Independents until the economy shows real improvement. Right now, he is functioning primarily on a base of Democratic support, which an escalation in Afghanistan has the potential to damage.
President Obama is probably not taking these political considerations into account when determining troop levels in Afghanistan, but given the impact that an escalation could have on human lives in other areas--specifically health care and climate change--it would not be a terrible idea if he did.