Stephen Biddle, a professor of international affairs at George Washington University, said the decision on post-2014 force levels is more important than the pace of 2013 withdrawals.
"The real issue is what you're ultimately going to draw down to -- what does the end of this road look like, not the weigh stations,'' Biddle said.
Officials have said the White House is considering a range of options that would leave between 5,000 and 10,000 troops beyond 2014, but it also is hoping for help from NATO allies. Those troops would limit their missions to training Afghan troops and hunting down terrorists.
Obama discussed the next phases of the drawdown with Karzai during a meeting in Washington last month, their first since Obama's re-election. They agreed to accelerate their timetable for putting Afghan forces in the lead combat role nationwide, moving that transition up from the summer to the spring.
A persistent worry is that pulling out of Afghanistan too quickly will leave the battle-scarred country vulnerable to collapse. In a worst-case scenario, that could allow the Taliban to regain power and revert to the role they played in the years before 9/11 as protectors of al-Qaida terrorists bent on striking the U.S.
Many Americans, however, are weary of the war, according to public opinion polls, and are skeptical of any claim that Afghanistan is worth more U.S. blood. Registered voters are roughly split between those who say the U.S. should remove all troops and those who favor leaving some troops in place for counterterrorism efforts, according to a recent Fox News poll.