From FactCheck.org:
A anti-abortion group is running an ad featuring a woman who says she survived a failed abortion and that "if Barack Obama had his way, I wouldn't be here." She's wrong. If she'd been born in Illinois, Illinois law would have protected her with or without the "born alive" legislation that Obama opposed and that this group supports.
The Obama campaign countered with its own false ad. It accused McCain of wanting to ban abortions even in cases of rape or incest, when in fact McCain has long supported such exceptions. Obama's ad also attributes the "born alive" attack ad to McCain, when it actually was sponsored by an independent group.
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