iraqi security forces struggling to take back the strategic stronghold of ramadi from isis terrorists. this comes as isis takes responsibility for a massive truck bomb at a vegetable market in baghdad. more than 30 people were killed. dozens more injured. let's get right to cnn's barbara starr, she's at the pentagon. you looked at ramadi. weeks since isis took it over. why has it been so difficult for those iraqi security forces that the u.s. is backing with air strikes and so on in training, why has it been so hard for them? >> it has been hard. ramadi is a must-win for the iraqis to prove they can boot isis out of there. but for the u.s., very strategically, it is also a must-win. the obama administration has to show they can get iraqi forces back into the field fighting and get them to take ramadi back. what have they been up to? they've been circling the city, trying to cut off isis supply lines into the city.