"I think there's a fair amount of intimidation of Iraqi forces by insurgents and you can do a lot of that without being on the inside," he said. Support for the insurgency has been fueled by discontent among Iraq's Sunni minority with the new government, and over time they have become very good at targeting U.S. forces, he added.
O'Hanlon stressed that both U.S. and Iraqi troops would be better served if security for the Iraqi forces was beefed up to perhaps retaliate against scare -- and death -- tactics.
RAND political scientist and terrorism expert Seth Jones went one step further, questioning the Iraqi security forces themselves.
"It's less of an infiltration issue than a loyalty issue," he said. Many of these security forces formerly belonged to brigades or militias and they still feel more allegiance to their brigade rather than to the Iraqi government, he explained.
Jones said that overall, having Iraqi forces fight with coalition partners hasn't been very successful, although he admits it is part of the nation-building process. That said, he warned that historically it takes nine years to effectively beat an insurgency, and so far the Iraqi resistance has stayed one step ahead of coalition forces, ambushing them every chance they get.
And Jones said he expects the situation to worsen.
"As U.S. forces begin to move out, that's when there will be real concern of infiltration among the compromised Iraqi forces," he said.