WASHINGTON - Record US casualties in Afghanistan are sparking White House fears that demands will mount for a premature military withdrawal, according to a media report. Citing unnamed senior administration sources, the Washington publication Politico reported Tuesday that aides to President Barack Obama are worried that liberal Democratic allies in Congress will demand an end to US involvement in Afghanistan before the president can post progress in the 8-year-old conflict. The Obama aides also reportedly are concerned that a narrow win for Afghan President Hamid Karzai in election results still being counted will bring his legitimacy as leader into question. They worry it may be likely that Afghanistan rather than healthcare reform will define the Obama presidencys early years, Politico said. Theres no question that the drumbeat is going to get louder and louder on the left, and youll see some fall-off on the right, Matt Bennett of the think-tank Third Way, told the publication. His supporters on the Hill are fighting a really serious political battle to keep the criticism under control. The aides also expressed concern that Afghan election returns, still being tallied, will result in a narrow re-election for President Hamid Karzai that could result in qualms about his legitimacy - Tehran II, as one official put it, in reference to the disputed Iranian election. The result: some think Afghanistan - not health care - will be the issue that defines the early years of the Obama administration. The Afghanistan conflict, which has gotten relatively little attention in part because Obama talks far more often about domestic concerns, is roaring back to the top of the Obama agenda as Congress is about to return from weeks of meetings with often unhappy voters. Senator Russ Feingold, a Democrat, last week called for a timetable to pull US troops out of Afghanistan - the same tactic he and other war opponents used to build congressional support for forcing an end to the Iraq war. But Obama officials - including National Security Adviser James Jones and Defence Secretary Robert Gates - know the problem is much bigger than Feingold and timetables. They anticipate a growing number of anti-war liberals will call, with increasing force, for an end to the conflict when lawmakers return. Cost could become an issue, too. With deficits high, there will be heavy pressure on Obama to find savings somewhere in 2010 - and war critics see Afghanistan as a good place to start.