But where does it end?

This argument is disturbingly reminiscent of Bush's claims about the "coalition of the willing" during the Iraq war. Yes, 41 countries have troops in Afghanistan. But only nine of them have more than 1,000 (the United States, Britain, Canada, France, Germany, Italy, the Netherlands, Poland, and Spain), and only two of those (the United States and Britain) have more than 5,000. Seven of the allies have sent a mere 10 troops or fewer.

When Bush left office, the United States contributed slightly less than half of the allied troops in Afghanistan. By the time Obama's escalation takes hold, this share will have risen to 70 percent. This is becoming more, not less, of an American war.

It is also not yet clear why President Obama picked 30,000 as the magic number of troops. Was it a compromise between the 40,000 recommended by Gen. Stanley McChrystal, commander of U.S. troops in Afghanistan, and some lower number reportedly suggested by Vice President Joe Biden? Was it driven, at least in part, by budgetary factors?

More to the point, what will they do once they get there? Gen. Nicholson said that the troops arriving soonest—7,000 Marines—will shore up the fight in central Helmand province. As others arrive, they'll be used for counterinsurgency campaigns in the eastern provinces, as trainers, or to provide a "quick counter punch" against the Taliban. We will presumably learn more when McChrystal and others begin their rounds of congressional hearings in the coming days and weeks.

That said, there were some very good things in tonight's speech.

Obama put the conflict in the context of the terrorist threat generally, not just to the United States but in a region seething with conflict and nuclear weapons.

His rationale is unapologetically reminiscent of Bush's justification for the 2007 "surge" in Iraq. (In fact, the "senior official" referred to Obama's buildup as a "surge.") These troops, Obama said in his speech, will "help create the conditions for the United States to transfer responsibility to the Afghans." Remember Bush's "As they stand up, we will stand down"?

The similarity is, in one sense, a bit creepy. On the other hand, maybe Obama really will link our tactical-military achievements with local-political gains. This line in the speech was particularly encouraging: "We will support Afghan ministries, governors, and local leaders that combat corruption and deliver for the people"—suggesting that if President Hamid Karzai doesn't come through on his recent promises, we will cultivate tribal or community centers of power, which, given the nature of Afghan society, are crucial to fending off insurgents in any case.

I also liked this statement: "As president, I refuse to set goals that go beyond our responsibility, our means, or our interests, and I must weigh all of the challenges that our nation faces." It outraged some TV commentators: How can Obama ask West Point's cadets for the ultimate sacrifice while shrugging that he can't afford to do everything on their behalf?

Well, the answer is that we can't afford to do everything for this particular battle; there are limits to our patience, stamina, and physical abilities; and it's good to acknowledge this up front. Maybe it will spur the Afghan leaders to get serious about their responsibilities; maybe it will spur Pakistan's leaders to get still more serious about the threat that the Taliban pose to their own survival. If they don't get serious, none of this matters, anyway.

Slate V: More Troops to Afghanistan