A little more than a year after Baghdad declared victory over the Islamic State group, many of its former supporters still walk the streets freely and Iraqis fear the militants might attempt a comeback.

President Donald Trump made a surprise visit to Iraq Wednesday amid criticism of his decision to withdraw American troops from neighboring Syria, a move which prompted the resignations of Defense Secretary Jim Mattis and Brett McGurk, the U.S. special envoy for the coalition to defeat ISIS.

Trump said that he had no plans to remove U.S. troops from Iraq but warned "the United States cannot continue to be the policeman of the world."

Secretary of State Mike Pompeo previously assured Iraqi Prime Minister Adil Abdul-Mahdi that the U.S. is still committed to supporting the fight against ISIS in the country.

But the White House has also ordered the Pentagon to draw up plans for a troop withdrawal from Afghanistan, officials told NBC News last week.

Hana’a al-Nuaimi remembers the three years she couldn't leave her home in the ISIS-conquered Iraqi city of Mosul without covering her face.

“Life now is much better than those dark days we lived under the ruling of ISIS,” she told NBC News. “We’re getting back to our normal lives, but very slowly.”

ISIS seized Mosul, Iraq's second-largest city, as well as one-third of the rest of the country before being toppled by an Iraqi military campaign that was backed by a U.S.-led coalition. Iraq announced the fight against ISIS was over on Dec. 9, 2017.

However, Al-Nuaimi is one of many Iraqis who haven’t been able to return to their former homes.

The widow lives with two of her children in eastern Mosul, unable to return to the city's west that still sits in ruins. They rely on her late husband’s pension of less than $400 a month.

Al-Nuaimi said people in the former ISIS stronghold are “suffering.”

Public services — including electricity — are not consistently available, many former supporters of ISIS still haven't been brought to justice, areas that were battle zones remain destroyed and 3 million people internally displaced by the war have yet to return home.

The presence of known terrorists in the city of Fallujah has Omar Hamad al-Dulaimi, 39, worried about whether the group could return.

“We know that many of the ISIS terrorists used to be members of Al Qaeda," he said. "Who knows, maybe in the future a new terror group would be formed under a different name, and those free terrorists would join it."

We have defeated ISIS in Syria, my only reason for being there during the Trump Presidency. — Donald J. Trump (@realDonaldTrump) December 19, 2018

I’ve done more damage to ISIS than all recent presidents....not even close! — Donald J. Trump (@realDonaldTrump) December 21, 2018

ISIS was never completely wiped out, according to Hisham al-Hashimi, an Iraq-based researcher in security and extremist groups. Attacks and bombings continue to occur throughout the country and remnants of ISIS still hold territory in remote and rural areas, he said.

While citizens have the right to anonymously provide information to authorities, there is a great deal of negligence on the part of Iraq’s intelligence service in handling or taking interest in tips, said security expert al-Hashimi. But violations, particularly by officers outside the capital, are difficult to prove to the leadership in Baghdad.

It’s resulted in fears of backlash for reporting suspected ISIS followers to authorities.

Al-Nuaimi recounted that someone was assassinated in her neighborhood after doing so.

Frustration with the government over issues ranging from security to services is becoming increasingly prevalent among Iraqis, according to Renad Mansour, a research fellow specializing in Iraq at the U.K.'s Chatham House think tank.

“Citizens are saying they are fed up with the process,” Mansour said. “So more and more people are going to the streets, people are protesting, people are looking at violent ways to take down the regime.”

Protests against the government turned deadly in the southern city of Basra earlier this year and Mansour said the situation is likely to erupt again unless basic services such as sanitation and water dramatically improve.

Global watchdog Transparency International ranks Iraq as one of the world's most corrupt countries, with a score of 18 out of 100 — with 0 being “highly corrupt.”

Dwindling faith in political institutions, compounded by a lack of economic opportunity and failing services, create an environment in which ISIS can thrive, Mansour said.

“It’s a dynamic organization, it can understand what the main grievances are and try to act as a representative for these disenfranchised populations,” Mansour added. “If corruption is rampant and if the economy doesn't improve, ISIS will be back."

Part of the problem is that the U.S. and allied forces have focused on territorial military tactics, not the underlying problems that lead people to join the group, Mansour said. The retreat from Syria is a clear example of that.

“If you bomb them and take over their territorial rule, it’s a job done. But what they haven’t tackled is why they are there and how to prevent them from coming back,” he said.

Iraq's security forces are now making the same errors, spending efforts responding to isolated attacks rather than looking at the broader context in which they're operating, al-Hashimi said.

“We continue to consider terrorist acts as side effects,” he said. “We keep attempting to cure this serious illness with sedatives… We are neglecting the source of the disease and the defect that generated the symptoms in the first place.”