Hillary Clinton, once a front-runner herself, warned Barack Obama's supporters Sunday that, though he leads John McCain in the homestretch of the presidential campaign, it's not over. "Sure, the polls show Barack and Joe [Biden] ahead now, and that's good news," said Clinton during her first joint appearance with her husband, former President Bill Clinton, to tout the Obama ticket. "But I don't pay much attention to polls - nobody should be lulled into any false sense of security."