Is Russia a threat — to its neighbors, to Europe, to the United States? What are the United States and its NATO allies prepared to do if Russia blackmails or attacks another sovereign democratic nation that is not a member of the alliance? Should the West continue to engage Russia or focus more on containing its ambitions?

Russia’s use of its potent air weaponry signals a “severe” and “dangerous escalation in the crisis,” the official, who spoke on condition of anonymity, told CNN. The official suggested that Russia is trying to destabilize Georgia politically in an effort to kill its chances of joining NATO.

Neither side showed any indication of backing down. Prime Minister Vladimir V. Putin of Russia declared that “war has started,” and President Mikheil Saakashvili of Georgia accused Russia of a “well-planned invasion” and mobilized Georgia’s military reserves.

The objectives of the war in Afghanistan have become increasingly uncertain in a conflict where Taliban leaders say they do not feel the need to control territory, at least for now, or to outfight American and NATO forces to defeat them — only to outlast them in a region that is in any case their home.