Democrats offered a different view from Bush's.

"On this grim milestone, it is worth remembering how we got into this situation, and thinking about how best we can get out," said Rep. John Dingell, D-Mich. "The tasks that remain in Iraq – to bring an end to sectarian conflict, to devise a way to share political power, and to create a functioning government that is capable of providing for the needs of the Iraqi people are tasks that only the Iraqis can complete."

In his remarks, Bush repeated his oft-stated determination to prosecute the war into the unforeseen future.

"The successes we are seeing in Iraq are undeniable, yet some in Washington still call for retreat," the president said, "War critics can no longer credibly argue that we are losing in Iraq, so now they argue the war costs too much. In recent months, we have heard exaggerated estimates of the costs of this war."

"No one would argue that this war has not come at a high cost in lives and treasure, but those costs are necessary when we consider the cost of a strategic victory for our enemies in Iraq," Bush said.

Bush has successfully defied efforts by the Democratic-led Congress to force troop withdrawals or set deadlines for pullouts. It is widely believed he will endorse a recommendation from Gen. David Petreaus, the top US commander in Iraq, for no additional troop reductions, beyond those already planned, until at least September.

The US now has about 158,000 troops in Iraq. That number is expected to drop to 140,000 by summer in drawdowns meant to erase all but about 8,000 troops from last year's buildup.

"If we were to allow our enemies to prevail in Iraq, the violence that is now declining would accelerate and Iraq could descend into chaos," Bush said, "Al-Qaida would regain its lost sanctuaries and establish new ones fomenting violence and terror that could spread beyond Iraq's borders, with serious consequences to the world economy.

"Out of such chaos in Iraq, the terrorist movement could emerge emboldened with new recruits ... new resources ... and an even greater determination to dominate the region and harm America," Bush said in his remarks, "An emboldened al-Qaida with access to Iraq's oil resources could pursue its ambitions to acquire weapons of mass destruction to attack America and other free nations. Iran could be emboldened as well with a renewed determination to develop nuclear weapons and impose its brand of hegemony across the broader Middle East. And our enemies would see an American failure in Iraq as evidence of weakness and lack of resolve."