President Barack Obama's decision to deploy another 30,000 U.S. troops to Afghanistan - and to also ask for more troops from coalition partners - has far-reaching strategic implications for the global effort to defeat violent extremists like the Taliban and al-Qaida.  Our Pentagon correspondent reports on this important turning point in the war in Afghanistan and the Obama presidency.

President Obama put it starkly in his long-awaited Afghan strategy speech Tuesday night.

"What's at stake is not simply a test of NATO's credibility - what's at stake is the security of our Allies, and the common security of the world," said President Obama.

The president said it is "vital" to send the additional troops, and to get them there by the middle of next year, a faster-than-expected deployment plan. 

"The president, in sending more troops to Afghanistan, is accepting responsibility for leadership of the war in Afghanistan," said Kim Kagan.

That is Kim Kagan, a military historian and president of the Institute for the Study of War.  She also served in a civilian advisory group assembled by General Stanley McChrystal, the top U.S. and NATO commander in Afghanistan, who made the troop request that resulted in the president's deployment decision.
"The truth of the matter is that we do not now have enough forces in Afghanistan to conduct a counterinsurgency campaign against the Taliban," he said.

Counterinsurgency involves securing the people, building the local government and security forces and fighting the militant forces, all at the same time.

Michael O'Hanlon of the Brookings Institution, just back from his latest visit to Afghanistan, endorses the decision to send more U.S. troops.  He says a counterinsurgency approach and General McChrystal's specific plan offer what he calls "a decent chance of success." 
"I think that there's a very strong case for a large number of additional troops," said Michael O'Hanlon. "The only detailed military analysis that's been done is McChrystal's."

General McChrystal said earlier this year that without more troops, the U.S. and allied effort in Afghanistan could fail.  But not everyone is convinced that sending more troops will result in success.  Among the skeptics is retired U.S. Army Colonel Andrew Bacevich, now a professor at Boston University.
"Counterinsurgency campaigns are long, drawn out, costly and tend to produce ambiguous outcomes," said Andrew Bacevich.

Bacevich expects no better outcome for the U.S. and allied effort in Afghanistan, particularly if the goal is, as President Obama reaffirmed Tuesday, to defeat al-Qaida and associated terrorist groups.
"I see no evidence that even if we succeed in Afghanistan, and I doubt we will, but even if we succeed in Afghanistan, we're not going to drive a stake through the heart of Jihadism," he said. "Again, more than likely, we'll probably simply exacerbate the problem."

Bacevich says the long-term presence of western troops in Islamic countries creates more terrorists than it kills or disarms.

Kim Kagan, at the Institute for the Study of War, acknowledges that even with more troops, expanded military training, a greater effort to strengthen the Afghan government and extensive operations against insurgent strongholds, success is not guaranteed.
"We do have to remember that war is a risky business and there is no assurance any particular force level will guarantee success," she said.

Kagan says success will depend on whether commanders use the troops effectively, and how the enemy responds, as well as how willing and able Afghan leaders are to fight corruption and build a more effective and popular government. 

And Afghanistan will have limited time to do that.  President Obama says he wants to begin transferring security responsibility to the country's government and military by July of 2011.  And although the president and other officials will not say how long the process will take after that, there is a timeframe many experts talk about.  Among them is Michael O'Hanlon.

"A rough approximation is about three years at the higher [troop] level, because that's about how long it will take to train, outfit, deploy and mentor these new Afghan security forces," he said.

But O'Hanlon says initial signs of success or failure should come much sooner, probably within a year.  Indeed, he says the counterinsurgency approach is already showing signs of success in areas where more U.S. troops have been sent this year.

Still, Andrew Bacevich thinks any expectation of a significant allied withdrawal in three years is overly optimistic.
"I'm very skeptical that we can achieve that kind of success in three years," said Bacevich. "I think it's far more likely that three years from now we'll have a very ambiguous situation, and the president is going to face a decision even more difficult than the one he is facing at the present moment."

Three years is a long time in American politics.  Kim Kagan says the president must make clear that the fight against the Taliban and associated groups has very high stakes not only for the Afghan people, but also for the region, and the world. 

"Defeating these extremist networks in series is of critical importance to the security of the United States and the security of Pakistan," said Kagan. "And is an essential prerequisite for success against Al-Qaida itself." 

And Kagan says it is up to other American leaders to help provide the time for the president's strategy to take hold.

"What I certainly would hope is that all of the leadership of the Democratic and Republican Parties would recognize that the war in Afghanistan is actually necessary for the defeat of al-Qaida, which poses a threat to the United States of America, and would give the president the leeway that he needs to actually fulfill his responsibilities as commander in chief," she said.

The analysts say it will certainly take the rest of President Obama's term in office - and perhaps all of a second term if he is re-elected - to even have a chance to fully, as he pledged earlier this month, "finish the job in Afghanistan."