Far from limited to a small group of "dead-enders" and Saddam "thugs" as Pentagon officials claim, the armed opposition to the US occupation in Iraq has reached the point where some experts say it threatens to become a full-fledged nationalist insurgency.
Bolstered by former Iraqi military and security personnel, today's insurgents are at the least conducting increasingly sophisticated coordinated attacks. In addition, they have built networks to recruit fighters, make weapons, and funnel funds from Iraqi businesses and charitable groups, military experts say.
Perhaps most important, insurgents are now motivated primarily by nationalism and Islam, rather than by loyalty to Saddam Hussein, they say.
US commanders are weighing moving tens of thousands more US troops into Iraq - as well as additional tanks and other armor - in an effort to curb unrest expected to surround the planned June 30 transfer of power to Iraqi authorities.
"The insurgency has worsened immeasurably," says Ahmed Hashim, an Iraq expert and professor of strategic studies at the Naval War College in Newport, R.I. For example, "the new insurgents showed a dramatic improvement in small-unit fighting skills" during recent violence in Sunni towns such as Fallujah, he said, testifying before Congress as a private citizen.
Coordinated attacks on convoys and troops, such as a devastating ambush in Ramadi this month that killed 12 US Marines, show insurgents in some areas are striking virtually as military units and withdrawing under covering fire, he says. "They have shown an ability to stand and fight, rather than merely to 'shoot and scoot' or 'pray and spray' as in the past."
Coupled with urban uprisings by Shiite militia that have also recruited former Iraqi enlisted soldiers and are now stockpiling weapons in mosques, the Iraqi insurgency has emerged as a multifront war for US forces nearly a year after Mr. Bush declared major combat over last May 1.
As heavy fighting reignited this week in Fallujah and Najaf, the number of US troops killed has roughly doubled to 120 this month, the deadliest since the war began. Meanwhile, deaths among Iraqi security forces and civilians, suicide bombings, and daily insurgent attacks all show upward trends.
"The trends on the security side are almost uniformly bad," says Michael O'Hanlon, a military analyst at the Brookings Institution who has been upbeat on the prospects for postwar Iraq.
To be sure, Iraqis have seen modest economic gains and improvements in basic services, and remain cautiously hopeful about their future, polls show. Yet the deterioration in security threatens to stifle, if not roll back, tentative progress on other fronts. In the debate over what has fueled the insurgency, military experts agree on some broad missteps: Unrealistic assumptions about how Iraqis would react to the occupation, the alienation of disbanded Iraqi soldiers, and too few US troops to ensure genuine security.
"We simply did not have enough manpower to police Iraq and protect the citizens while at the same time fully engage in combating the insurgency," says Mr. Hashim.
Beginning last fall and culminating in the winter with Mr. Hussein's capture, the insurgency's composition shifted from what the Pentagon calls "former regime loyalists" to Iraqis motivated by nationalism and Islam, as clerics increasingly stepped into the local power void, experts say. In Sunni areas, disgruntled, jobless Iraqi military and intelligence personnel used their expertise in weaponry and explosives to bolster the proficiency of insurgents.
Their ranks have swollen with young men from Sunni Arab tribes that felt both disenfranchised and angered by harsh US military tactics in the Sunni Triangle. Meanwhile, an influx of small numbers of foreign terrorists and Sunni extremists willing to carry out suicide attacks served as a "force multiplier" for the insurgency.
"Sunni tribesmen ... have become the principal popular support for most of the Sunni Arab and foreign insurgents," says Kenneth Pollack, a Middle East specialist at the Brookings Institution. Like other experts, Mr. Pollack stresses the existence of a popular base of support that is sustaining Iraqi insurgents. "We should always remember Mao Zedong's parable of the sea and the fish; the people are the sea and the guerrilla is the fish, and as long as the sea is hospitable to the fish, you will never catch them all."
At the same time, Shiite clerics asserting their influence after the fall of the regime steadily built up their militia and support networks. In Baghdad's sprawling Sadr City, for example, the anti-US cleric Moqtada al Sadr moved into former Baath Party neighborhood offices and systematically recruited poor, unemployed youth with offers of money and welfare for their families.
Today, military sources say Sadr's Mahdi Army has 7,000 to 10,000 men. Iran has agents in Najaf and Karbala who are providing arms and training to various Shiite militia, the sources say.
Some low-level cooperation is underway between Shiite and Sunni insurgents, says Hashim, and Shiite militiamen from Sadr City have even infiltrated Fallujah to battle coalition forces, he adds.
To head off worse violence, experts say the US must urgently add tens of thousands of troops to the 135,000 now in Iraq in order to uproot enemy fighters and better protect Iraqi civilians.
The top US commander in the Middle East, Gen. John Abizaid, this month retained 20,000 troops scheduled to leave Iraq and says he may need more. Tanks and other armored vehicles, which were left at US bases when fresh troops such as the 1st Cavalry Division rotated into Iraq this spring, may now be brought into the country. "We are doing some planning for follow-on forces," said Gen. Richard Myers, chairman of the Joint Chiefs of Staff, this month, adding that the military may beef up existing forces by replacing some Humvees with tanks.