Negative TV ads hit the airwaves in Iowa and New Hampshire this weekend, marking the start of mudslinging in the 2008 presidential campaign.

A pro-abortion Republican group is shelling out $100,000 dollars for TV spots in the two early-voting states. The ads target former Massachusetts Governor Mitt Romney's record on the issue.

Several campaign veterans say the negative advertising against Romney may open the door to bigger ad buys to target other candidates and topics.

While negative advertising is possible on the Democratic side, strategists say they're not surprised to see it start in the Republican race. Front-runners Romney and Rudy Giuliani have left a long trail of changed positions on key issues.

As a University of New Hampshire political scientist puts it, "It's a target-rich environment for negative ads."