The left is already doubting Obama's Afghan surge.

The regents are on the ground and commanders are crafting new battle plans: President Obama is girding for a war surge in Afghanistan. Let's hope he's willing to see it through when his most stalwart supporters start to doubt the effort and rue the cost.

As a statement of principle, the new Administration's preoccupation with Afghanistan signals a welcome commitment to what has been known by that out-of-favor phrase "global war on terror." The Taliban claimed responsibility last week for coordinated suicide attacks in Kabul, which killed 28 people and reinforced perceptions that security is eroding. America's recent success in Iraq showed that the key to victory lies in shifting those perceptions. That means improving security.

More U.S. troops will likely be needed, and Central Command General David Petraeus is undertaking a review of goals and the resources to meet them. Mr. Obama has talked about doubling forces by another 30,000, and we hope he's willing to give his Afghan commander, General David McKiernan, the number he needs to clear and hold areas and protect the population. However, size of force matters less than having the proper counterinsurgency strategy for a conflict that is different than Iraq.

Among other useful things, Mr. Obama's surge may help to educate his friends on the political left about Islamist terror. The National Security Network, an outfit that never missed an opportunity to bash President Bush, has quickly come into line behind the new President. The group says Mr. Obama's strategy must be focused "first and foremost on preventing the Afghanistan-Pakistan region from becoming a staging ground for terrorist attacks against the U.S. and other nations or a source for instability that could throw Pakistan into chaos."

Sounds good to us -- and sounds a lot like the Bush strategy. America's goal isn't to turn a backward Central Asian country into the next Switzerland, but to keep al Qaeda and its Taliban allies from using it as a safe haven. Toward that end, the U.S. and its allies can help build Afghanistan's institutions and army and help a weak Pakistan government flush out the terrorists in its wild west.

No doubt the strategy can be tweaked. That started well before Mr. Obama's election, as America took back ownership of the Afghan mission from an unwieldy NATO command. Though Britain and Canada pull their weight, Secretary of Defense Robert Gates has learned that Americans can't count on Europe to fill the troop and equipment gaps, so the U.S. did.

Also like the Bush Administration, Team Obama recognizes the Pakistan dimension to the Afghan problem -- even calling the place "Afpak." The Taliban came back in the past three years only after finding sanctuary around Quetta, in southern Pakistan, and in the country's northwest tribal regions. The U.S. has also won Islamabad's sotto voce cooperation to strike terror leaders, though more should be done around Quetta.

Mr. Obama's special envoy, Richard Holbrooke, has been in Afpak for a week's fact-finding. Before arriving, he said, "In my view it's going to be much tougher than Iraq." Even by Holbrookeian standards, that's hyperbole. The government in Kabul isn't in danger of collapsing, the Taliban isn't popular where it has ruled, and the insurgents are no match for the U.S.-led force on the battlefield.

Ultimately, as in Iraq, the Afghans will need to stand up more for themselves. That may take a while. But start with expanding the increasingly able Afghan army, a bright spot. The force of 80,000 is too small for a country the size of Texas and bordered by enemies. The police are a shambles, alas. Corruption, narco-trafficking, a weak central government: Afghanistan shares vices with other Western protectorates like Bosnia, and could improve on all counts.

However, notwithstanding President Obama's swipe last Monday that "the national government seems very detached from what's going on in the surrounding community," the rulers in Kabul are legitimate. Hamid Karzai has tolerated too much corruption, but any change of leadership should come from an Afghan challenge, not a U.S. desire to play kingmaker. Mr. Obama and Vice President Joe Biden -- who stormed out of a meeting with Mr. Karzai last year -- need to avoid JFK's mistake of toppling South Vietnam ally Ngo Dinh Diem.

The Obama team wants to play up Afghanistan's troubles so it can look good by comparison a year from now. But soon enough Mr. Obama will own those troubles, and talking down Afghanistan carries risks. Our allies and the American people may come to doubt that the conflict is winnable, or worth the cost.

Already, canaries on the left are asking a la columnist Richard Reeves, "Why are we in Afghanistan?" The President's friends at Newsweek are helpfully referring to "Obama's Vietnam." Mr. Obama may find himself relying on some surprising people for wartime support -- to wit, Bush Republicans and neocons.