For the past couple of weeks, we have been debating whether the GOP presidential field, with its talk of withdrawal from Afghanistan, was slipping into isolationism. Wednesday night, President Obama made clear that if his Republican challengers want the “come home America” vote, they’ll have to wrest it from him. Listen to the president’s words: “Over the last decade, we have spent a trillion dollars on war, at a time of rising debt and hard economic times.” “Let us responsibly end these wars, and reclaim the American Dream.” “Take comfort in knowing that the tide of war is receding.” “America, it is time to focus on nation building here at home.” Not a word about “victory” in Afghanistan or even “success.” This was a speech not about winning, but withdrawal. Eat your heart out, Jon Huntsman.

The withdrawal plan the president announced last night was an exercise in pure politics designed to appeal to growing popular sentiment. There is no military reason for these troop reductions. As the president himself pointed out, “We have ended our combat mission in Iraq, with 100,000 American troops already out of that country,” and “in Libya . . . we do not have a single soldier on the ground.” This means there is no “stress on the force” that makes these troop reductions an urgent necessity. They are being made for domestic political reasons, plain and simple. Even the timing the president laid out is suspect. Why, for example, will the final surge forces be brought home in September 2012 — just in time for the presidential election? To get those forces home in September requires beginning their rotations home many months before – in the middle of the spring and summer fighting season, when our commanders on the ground need them most.

But even the political rationale for these troop withdrawals does not make much sense. Consider: Today, the United States has about 100,000 troops in Afghanistan. When the president’s drawdown is completed next year, we will have about 70,000 troops in Afghanistan. Will the advocates of retreat on the left be any less opposed to the Afghan war with 70,000 troops in country than they were with 100,000? Of course not.

Drawing down these forces will have little political impact here at home – but it could have a devastating military impact on the ground in Afghanistan. It will make it harder to hold the territory we have taken at great cost from the Taliban. It will embolden our enemies by sending the signal that we care more about leaving than winning. It will dispirit the Afghan people and make them less likely to risk their lives helping us against the Taliban — because they see that we are leaving and the Taliban is staying. It will undermine our coalition, giving a green light for our NATO allies to pull their forces out prematurely as well. In short, it will endanger the success of the mission. If Afghanistan goes off the rails in the months ahead, the political consequences for Obama could be far worse than the price he would pay from the left for failing to removing 30 percent of our troops in Afghanistan.

And Afghanistan could well go off the rails as a result of the president’s decision. Note that in his speech, Obama said that our military had taken “a number of [the Taliban’s] strongholds” — meaning that many still remain. That is because the president only sent about 30,000 surge troops to Afghanistan – significantly below the number his commanders requested. This forced our troops to put off critical operations — focusing on driving the Taliban from southern Afghanistan (which was in imminent danger of falling to the enemy) while delaying planned clearing operations in eastern Afghanistan. In the months ahead, our commanders must somehow manage to hold the ground they gained in the south against a Taliban counteroffensive, while undertaking those delayed operations to drive the enemy from its eastern sanctuaries. Last night, the president told them they must do so while sending home the 30,000 surge forces he had given them for this purpose. That may be an impossible mission.

When President George W. Bush announced a drawdown of U.S. forces in Iraq in September 2007, he said he was doing so because “General Petraeus believes we have now reached the point where we can maintain our security gains with fewer American forces.” President Obama made no such claim about Petraeus last night. Bush also made clear that “the principle guiding my decisions on troop levels in Iraq is ‘return on success.’ The more successful we are, the more American troops can come home. And in all we do, I will ensure our commanders on the ground have the troops and flexibility they need to defeat the enemy.” Obama made no such promise last night. His approach could be best described as “return before success” – and the result could very well be defeat.