US President Barack Obama on Friday moved to fulfill the defining promise of his campaign, saying all US combat troops will be withdrawn from Iraq by the end of August 2010. "I have come to speak to you about how the war in Iraq will end," Obama declared in his remarks to Marines and military leadership at the North Carolina base. But in the same speech, Obama announced that the vast majority of those involved in the pullout will not leave this year. Obama also said that tens of thousands of US personnel will remain behind afterward. "The most important decisions that have to be made about Iraq's future must now be made by Iraqis," the president said at the sprawling Camp Lejeune, North Carolina, base, which is about to deploy thousands of troops to the US's other war front, in Afghanistan. Senior Obama administration officials had said earlier that of the roughly 100,000 US combat troops to be pulled out of Iraq over the next 18 months, most will remain in the war zone through at least the end of this year to ensure national elections there go smoothly. The pace of withdrawal means that although Obama's promised pullout will start soon, it will be backloaded, with most troops leaving in the last few months of the time frame. And even after the drawdown, a sizable residual force of 35,000 to 50,000 US troops will stay in Iraq under a new mission of training and advising Iraqi security forces, providing protection and support for US and other civilians working on missions in Iraq, and targeted counterterrorism. The Iraq war helped fuel Obama's presidential bid. Polls show that most Americans think the war was a mistake. More than 4,250 US military members have died in the nearly six years since the United States invaded Iraq and toppled the regime of Saddam Hussein. Total Iraqi deaths are unknown but number in the tens of thousands and are perhaps above 100,000. The Aug. 31, 2010, end date for Iraq war combat operations is slower than Obama had promised voters as a candidate. The timetable he pledged then would have seen combat end in May 2010. Regardless, it is a hastened exit, something Obama called a necessity, both for the future of Iraq and to allow the US to refocus its attention more firmly on Afghanistan. "America can no longer afford to see Iraq in isolation from other priorities: We face the challenge of refocusing on Afghanistan and Pakistan; of relieving the burden on our military; and of rebuilding our struggling economy and these are challenges that we will meet," he said. Obama applauded the military for its role in creating an improved situation in Iraq, where violence is down significantly in Baghdad and most of Iraq and US military deaths have plunged. He also acknowledged that many problems remain in the country and said "there will be difficult days ahead." Those include violence that will remain "a part of life," political instability and fundamental unresolved questions, a large displaced and destitute citizenry, tepid support for Iraq's fragile government in the neighborhoods and the stress of declining oil revenues. But, the president said the US cannot continue to try to solve all Iraq's problems. "We cannot rid Iraq of all who oppose America or sympathize with our adversaries," he said. "We cannot police Iraq's streets until they are completely safe, nor stay until Iraq's union is perfected. We cannot sustain indefinitely a commitment that has put a strain on our military, and will cost the American people nearly a trillion dollars." He emphasized that an end to the war does not mean the US plans to withdraw from its interests in the region. He promised intensified diplomatic and humanitarian efforts. "The end of the war in Iraq will enable a new era of American leadership and engagement in the Middle East," Obama said. War critics were ready to hear Obama's public words, which came just three weeks shy of the war's 6-year anniversary. But the size of the force to be left behind after the combat-troop drawdown did not please leaders of Obama's own Democratic Party, who had envisioned a fuller withdrawal. Obama personally briefed House and Senate members of both parties about his intentions behind closed doors Thursday. Obama had said all along he would keep a residual force in Iraq. "When they talk about 50,000, that's a little higher number than I had anticipated," Senate Majority Leader Harry Reid said, echoing many others. Republican Sen. John McCain, who lost the presidential election to Obama, offered his support for the president's plan while saying that the residual force would still go on combat patrols alongside Iraqis. "They'll still be in harm's way," he said in an interview. "There's no doubt about it." Defense Secretary Robert Gates and Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, told lawmakers in the White House briefing that ground commanders in Iraq believe the plan poses only a moderate risk to security, McCain said. Obama also on Friday notified two key figures of his pending announcement: Iraqi Prime Minister Nouri al-Maliki and, minutes before taking the podium, former President George W. Bush. From the Jan. 20 start of his presidency to his deadline for ending the combat mission, Obama has settled on a 19-month withdrawal. He had promised the faster pace of 16 months during his campaign but also said he would confer with military commanders on a responsible exit strategy. Officials said Thursday that the timetable Obama ultimately selected was the recommendation of all the key principals - including Gates and Mullen. The timeline was settled on as the one that would best manage security risks without jeopardizing the gains of recent months. In any case, the last of any kind of US troops must be out of Iraq no later than Dec. 31, 2011. That is the deadline set under an agreement the two countries sealed near the end of Bush's presidency. Obama has no plans to extend that date or pursue any permanent troop presence in Iraq. With 142,000 US troops in Iraq, Obama plans to withdraw most of them; the total comes to roughly 92,000 to 107,000, based on administration projections. Administration officials spoke about Obama's Iraq decision under condition of anonymity to discuss details of the strategy ahead of the announcement. They said Obama would not set a more specific schedule, such as how many troops will exit per month because he wants to give his commanders in Iraq flexibility. "They'll either speed it up or slow it down, depending on what they need," said one official. Yet the officials made clear Obama wants to keep a strong security presence in Iraq through a series of elections in 2009, capped by national elections tentatively set for December. That important, final election date could slip into 2010, which is perhaps why Obama's timetable for withdrawing combat troops has slipped by a few months, too. The officials said that Gen. Ray Odierno, the top American commander in Baghdad, wanted flexibility around the elections. "The president found that very compelling," one said. The senior administration officials sought to describe Obama's decision-making process as one that was not driven by his political promise to end the war. They said he consulted extensively with his military team while interagency government teams reviewed the options.