Some 4,000 U.S. Marines accompanied by 650 Afghan forces ripped into Afghanistan's southern Helmand Province on Thursday.

Their stated intention was to drive out the Taliban, well installed in Helmand and other Afghanistan provinces, and to assure the population of Helmand of their long-term security. In addition, given that the province is one of Afghanistan's principal opium-producing areas and that sales of it provide the Taliban with a substantial portion of their financing, the Marines will also seek to extirpate to the degree possible poppy cultivation there.

Both of these goals will require the Marines to establish an at least semi-permanent presence there, as opposed to the in-and-out approach that U.S. and other NATO forces have taken to Helmand until now, driven by a shortage of forces in-country as well as the dangers involved in setting up there. President Barack Obama decided to raise the level of U.S. forces in Afghanistan by 20,000 to 68,000.

Achievement of these U.S. goals is likely to involve further U.S. casualties in Afghanistan, adding to the more than 700 already lost, as well as considerable financial cost.

The question is, does it make sense? U.S. war in Afghanistan did make sense in 2001 in the wake of the 9/11 attacks, mounted from there by al-Qaida, which was hosted by the Taliban government. U.S. and Afghan forces combined to drive al-Qaida and the Taliban out by early 2002. However, the administration of President George W. Bush did not consolidate democratic rule and economic development in post-Taliban Afghanistan, choosing instead to launch the war that is still under way in Iraq.

The Taliban's response to the U.S. thrust into Helmand will likely be to fall back and fade into the population, awaiting the Americans' departure rather than engaging with them militarily and taking the casualties. Then the question becomes how long the American forces will be willing to stay in Helmand? The force mix in the incursion, six Americans to each Afghan, is indicative of both the level of commitment and perhaps the level of readiness of Afghan forces after eight years of U.S. training.

The larger question is how long is the United States prepared to stay engaged in Afghanistan, in Helmand Province or anywhere else. The British gave up on it in 1919. The Soviet Union withdrew in 1989. How long is America prepared to stay, particularly given its other commitments around the world, as the cost in American lives and financial resources rises?

Mr. Obama would do well to continue to gauge American public opinion carefully to remain current on the level of popular support for his war in Afghanistan as it escalates.