And the role of Shiite militias in the new operation brings fears that sectarian tensions could be stirred up in Anbar, Iraq's Sunni heartland.
ISIS militants, meanwhile, have shown a willingness to adapt their tactics to focus on gaps in their enemies' defenses.
The Iraqis' will to fight
The commitment of Iraqi security forces to the battle with ISIS has been in the spotlight since U.S. Defense Secretary Ash Carter told CNN
that they "showed no will to fight."
The White House struck a different note Tuesday, with press secretary Josh Earnest saying the new operation was "a clear indication of the will of the Iraqi security forces to fight."
The Anbar campaign
is still in its early stages, with no big move reported so far to try to take Ramadi.
So far, the Iraqi units are just conducting probing attacks against ISIS, U.S. officials said. But Iraq's Defense Ministry says the forces have surrounded ISIS in Ramadi and cut off key supply routes.
The real test will come when they go on the offensive to try to reclaim Ramadi.
The role of the Shiite militias
Complicating that effort is the major part expected to be played by predominantly Shiite paramilitary forces, the Popular Mobilization Units.
Some analysts say they fear a sectarian bloodbath.
"I cannot imagine anything more carefully calculated to permanently split this country apart, the country of Iraq apart, than a Shia-led military effort into a completely Sunni area," said Ryan Crocker, a former U.S. ambassador to Iraq.
The militias even gave their operation a sectarian undertone, naming it for Imam Hussein, one of Shiite Islam
's most venerated figures. "Evoking the name of the grandson of the prophet, Hussein, is an insult to Sunni Muslims," said CNN security and intelligence analyst Robert Baer.
But other experts say the concerns of a flare-up in Sunni-Shiite tensions are overblown.
Lt. Col. James Reese, a retired Delta Force commander, said using a mixture of Iraqi military and police along with the Shiite militias eventually worked in the push to retake the city of Tikrit from ISIS in March.
"It wasn't pretty. It was very ugly. But it was ... successful," he said. "I think it's the same model you're going to see out west in Al Anbar."
Reese, who recently spent time with the Iraqi military, said that soldiers on the ground he spoke to, both Sunni and Shiite, saw ISIS as "a common enemy" that they wanted to defeat. "I've seen them," he said. "I've seen Sunni and Shia fight together on top of a roof in Tikrit."
New ISIS tactics
The Iraqi forces that move in on Ramadi will have to contend with ISIS jihadists' evolving battlefield tactics.
Analysts say that for its conquest of Ramadi, the militant group called in extra fighters from Syria
, used snipers and suicide bombs in new ways, and dug tunnels to get into parts of the city and blow up Iraqi fortifications.
"They're scouting the Iraqi security forces and gaining intelligence from reconnaissance," said retired Lt. Gen. Mark Hertling, a former commander of U.S. Army forces in Europe. "They're understanding the capability of the Iraqi security forces -- to include coalition air power. And they are adjusting their tactics to counter that."
They have also started moving in small groups, making it harder for U.S. warplanes to find them, and staying off social media.
"They have seen that there can be operational consequences to essentially live-tweeting or live-posting regarding their operations," said Daniel Milton, a research associate at the Combating Terrorism Center at the U.S. Military Academy at West Point.
The effectiveness of U.S.-led airstrikes
ISIS' adaptive tactics are among the challenges the U.S. military and its allies face in their air campaign to help the Iraqi forces on the ground.
U.S. officials insist the Iranian-backed Shiite militias must remain under the control of the central Iraqi government, a proposition that in the past has been difficult.
The American fear is that a U.S. airstrike could accidentally hit a Shiite militia group, a situation likely to provoke a furious reaction.
The U.S. military will also launch strikes only when it has its own intelligence regarding ground targets to avoid hitting civilians, officials say.
Some experts suggest that needs to change.
"I think on the air power side, we're probably going to have to be a little more aggressive and less cautionary about collateral damage. We're going to have to step it up," said retired Adm. James Stavridis, a former NATO supreme allied commander.
One Shiite militia leader on the ground told CNN's Arwa Damon that his fighters aren't banking on any help from the U.S. military.
"Anyone who depends on American support is depending on a shadow," said Hadi al-Amiri, who commands the Badr Brigade. "The dependence by the central government on the United States is one of the reasons we lost Ramadi."
The support of the Sunni tribes
While the Shiite militias are at the forefront of the effort to retake Anbar, the Sunni tribes that have been fighting ISIS there for more than a year have their grievances.
They've been calling for better weapons supplies for months, but with little result.
Iraq's Shiite-led government in Baghdad has "not provided the resources, the equipment necessary for the tribesmen," said U.S. Rep. Ed Royce, R-California, the chairman of the House Foreign Affairs Committee.
He said the recently passed National Defense Authorization Act mandates that "some of the aid that we put through Baghdad go directly to the Kurdish
forces and to the Sunni tribes."
The reluctance of the central Iraqi government to funnel arms to the Sunni tribesman -- amid claims the weapons could end up in the hands of ISIS -- has deepened resentment among the Sunni population.
Some tribesman have been at the forefront of the battle against ISIS, but others have agreed to fight alongside ISIS or remain neutral.