Following up on Plummer's article below... During the Vietnam War, our troop levels outnumbered the VC guerrillas by around 3-to-1, according to Robert McNamara's July, 1965 memorandum to President Johnson. That ratio shifted only slightly as the war escalated.
And we got clobbered.
Partly because the recommended "winnable" ratio was actually 10-to-1. Ten U.S. soldiers to every one VC guerrilla.
If the 200,000 Iraqi insurgent number is correct, and if the old Vietnam ratio still applies (both are guerrilla wars), we'd need 2 million troops to secure the country and to "smoke out" the evildoers.
And that would mean a draft.
Additional reading on guerrilla warfare here.