There are two big news items from Obama's speech tonight: a surge of 30,000 troops in Afghanistan and a withdrawal of combat troops by the end of 2011. What you consider to the most important will probably depend on your political stripes─and the president best be prepared for incoming from both sides.
Republicans will no doubt hit him on the timetabled withdrawal. Conservatives, including John McCain, have long argued that a withdrawal should be based on conditions on the ground and that telegraphing your exit to the enemy is a recipe for disaster. Expect Republicans to criticize him heavily on this point, arguing that Afghans will ally around local warlords rather than cooperating with Americans because if they know the U.S. is leaving, they won't believe their long-term safety is guaranteed any other way. They'll also say that this short exit time frame will fracture relations with Pakistan, which, among other things, is a nation whose trust is difficult to maintain but whose intelligence is vital to American national security.
On the left, the withdrawal announcement will satisfy some doubters whose opposition to the war is increasingly vocal. But that won't prevent Obama from being roundly criticized for committing more troops in the first place. Although the president was at pains to explicate the link between the war in Afghanistan and American national interest, many critics on the left have thought for some time that the war is no longer worth fighting. They'll simply see more loss of life. They'll also see more suffering on the part of the Afghan people, which arguably provides more fodder for extremist recruiters.
As usual, the president's speech was eloquent, if less poetic than normal. This was an austere speech where his usual flowery touches would appear discordant. It wasn't a triumphant announcement with smartly uniformed troops lined up as a backdrop. There weren't wild bursts of applause. Instead was one man, making a deadly serious case for his actions, in full knowledge that friends and foes alike will attack him for it. Standing there by himself, it really did seem like loneliest job in the world.