Coalition troops have met fierce resistance from Iraqi military and paramilitary forces as they push north toward Baghdad. Gwen Ifill discusses the roots of that resistance with profesors Ahmed Al-Rahim and Rashid Khalidi.

Smoke continued to billow out of Baghdad Friday after U.S.-led forces unleashed the heaviest bombardment of the Iraqi capital in days, using B-52 bombers to drop two 4,700-pound, satellite-guided "bunker-busting" bombs on Iraqi targets.