WEST POINT, N.Y. (AP) âÄî Declaring âÄúour security is at stake,âÄù President Barack Obama ordered an additional 30,000 U.S. troops into the long war in Afghanistan on Tuesday night, but balanced the buildup with a pledge to an impatient nation to begin withdrawing American forces in 18 months. In a prime-time speech at the U.S. Military Academy, the president said his new policy was designed to âÄúbring this war to a successful conclusion.âÄù The troop buildup will begin almost immediately âÄî the first Marines will be in place by Christmas âÄî and will cost $30 billion for the first year alone. âÄúWe must deny al-Qaida a safe haven,âÄù Obama said in articulating U.S. military goals for a war that has dragged on for eight years. âÄúWe must reverse the TalibanâÄôs momentum. … And we must strengthen the capacity of AfghanistanâÄôs security forces and government.âÄù The president said the additional forces would be deployed at âÄúthe fastest pace possible so that they can target the insurgency and secure key population centers.âÄù Their destination: âÄúthe epicenter of the violent extremism practiced by al-Qaida.âÄù âÄúIt is from here that we were attacked on 9/11, and it is from here that new attacks are being plotted as I speak,âÄù the president said. It marked the second time in his young presidency that Obama has added to the American force in Afghanistan, where the Taliban has recently made significant advances. When he became president last January, there were roughly 34,000 troops on the ground; there now are 71,000. ObamaâÄôs announcement drew less-than-wholehearted support from congressional Democrats. Many of them favor a quick withdrawal, but others have already proposed higher taxes to pay for the fighting. Republicans reacted warily, as well. Officials said Sen. John McCain, who was ObamaâÄôs Republican opponent in last yearâÄôs presidential campaign, told Obama at an early evening meeting attended by numerous lawmakers that declaring a timetable for a withdrawal would merely send the Taliban underground until the Americans began to leave. As a candidate, Obama called Afghanistan a war worth fighting, as opposed to Iraq, a conflict he opposed and has since begun easing out of. A new survey by the Gallup organization, released Tuesday, showed only 35 percent of Americans now approve of ObamaâÄôs handling of the war; 55 percent disapprove. âÄúAfter 18 months, our troops will begin to come home,âÄù he said flatly. In eight years of war, 849 Americans have been killed in Afghanistan, Pakistan and neighboring Uzbekistan, according to the Pentagon. In addition to beefing up the U.S. presence, Obama has asked NATO allies to commit between 5,000 and 10,000 additional troops. He said he was counting on Afghanistan eventually taking over its own security, and he warned, âÄúThe days of providing a blank check are over.âÄù He said the United States would support Afghan ministries that combat corruption and âÄúdeliver for the people. We expect those who are ineffective or corrupt to be held accountable.âÄù As for neighboring Pakistan, the president said that country and the United States âÄúshare a common enemyâÄù in Islamic terrorists. He added his policy will be to strengthen PakistanâÄôs capacity to target terrorists, and he said the U.S. has âÄúmade it clear that we cannot tolerate a safe haven for terrorists whose location is known.âÄù Most of the new forces will be combat troops. Military officials said the Army brigades were most likely to be sent from Fort Drum in New York and Fort Campbell in Kentucky; and Marines primarily from Camp Lejeune in North Carolina. Officials said the additional 30,000 troops included about 5,000 dedicated trainers, underscoring the presidentâÄôs emphasis on preparing Afghans to take over their own security. They added the president is making clear to his generals that all troops, even if designated as combat, must consider themselves trainers. These aides said that by announcing a date for beginning a withdrawal, the president was not setting an end date for the war. But that was a point on which McCain chose to engage the president at a pre-speech meeting with lawmakers before Obama departed for West Point. âÄúThe way that you win wars is to break the enemyâÄôs will, not to announce dates that you are leaving,âÄù McCain said later. ObamaâÄôs address represents the beginning of a sales job to restore support for the war effort among an American public grown increasingly pessimistic about success âÄî and among some fellow Democrats in Congress wary of or even opposed to spending billions more dollars and putting tens of thousands more U.S. soldiers and Marines in harmâÄôs way. Sen. Russ Feingold, D-Wis., and liberal House Democrats threatened to try to block funding for the troop increase.