Islamic State militants. Militant website via AP

The Pentagon inspector general issued a report to Congress saying that the Islamic State is again growing in power in Syria and Iraq, with approximately 14,000 to 18,000 militants.

The report specifically said President Donald Trump's decision to rapidly draw down troops in Syria and pull diplomatic staff from Iraq increased instability and allowed the militants to regroup.

Former Special Presidential Envoy Brett McGurk, who resigned following the drawdown announcement, has repeatedly warned of this scenario, saying that Trump's policies would lead to chaos and "an environment for extremists to thrive."

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A report from the Pentagon inspector general found that President Donald Trump's decision to rapidly pull troops out of Syria and divert attention from diplomacy in Iraq has inadvertently aided the Islamic State's regrouping in Syria and Iraq.

The Department of Defense's quarterly report to Congress on the effectiveness of the US Operation Inherent Resolve mission said that "ISIS continued its transition from a territory-holding force to an insurgency in Syria, and it intensified its insurgency in Iraq" - even though Trump said ISIS was defeated and the caliphate quashed, The Wall Street Journal reported.

Many officials and experts have repeatedly warned that a rapid US withdrawal from Syria would enable ISIS to regroup into an insurgency after their battlefield defeats by the US-led coalition.

Read more: Trump didn't bother to tell his top general in the Middle East that he was going to pull troops out of Syria

The IG's report also explicitly said the troop drawdown in Syria, which Trump announced at the end of last year, contributed to instability in the region. The drawdown, which prompted the resignation of Defense Secretary Jim Mattis, left the US's Syrian partners in the lurch, without the training or support they needed to confront a resurgent ISIS. In Iraq, the Iraqi security forces lack the necessary infrastructure to fight off ISIS for sustained periods.

Read more: US prosecutors charged an American with traveling from New York to Syria to be an Islamic State sniper

ISIS is estimated to have 14,000 to 18,000 combatants, according to the report, who are carrying out assassinations, suicides, crop burnings, and ambushes in Iraq and Syria - different from the large-scale attempts to seize territory since 2014 but a violent threat to civilians in both countries nonetheless.

Perhaps more importantly, ISIS is again generating revenue by extorting civilians in both countries, kidnapping for ransom, and skimming money from rebuilding contracts. This decentralized method of income generation - unlike the detailed tax and revenue system ISIS employed during its caliphate - makes the income more difficult to track.

The al-Hol refugee camp in Syria seems to be a perfect storm for ISIS recruitment - thousands of internally displaced people, security forces unable to guard the area against insurgents, and little US support to maintain safe conditions or counter ISIS propaganda.

The Trump administration's decision to focus its attention on Iran reduced its capacity to effectively counter ISIS in Iraq and Syria, according to Brett McGurk, the former special presidential envoy for the Global Coalition to Counter ISIS who served under Presidents George W. Bush, Barack Obama, and Donald Trump.

McGurk, like Mattis, resigned his post after Trump announced his drawdown. In a January op-ed, he warned that Trump's policies in the region would give "new life" to ISIS and other US adversaries, and that the decision would "precipitate chaos and an environment for extremists to thrive," exactly what the IG's report said was happening on the ground.

The US has the same expectations of success in Syria, but now without putting in the resources to ensure that success; with around 1,000 troops in Syria, it expects to counter ISIS, stop Syrian President Bashar Assad from developing weapons of mass destruction, and counter Iranian influence.

The decision to pull nonemergency personnel from Iraq reduced US diplomatic influence there, and, according to the State Department, reduced humanitarian groups' ability to offer support.

Trump campaigned in part on a promise to withdraw the US from conflicts in the Middle East, as part of his "America First" policy. But his shortsighted decision-making based on that premise doesn't just destabilize Iraq and Syria, it also has the potential to do the same in Afghanistan, where the US is negotiating with the Taliban to withdraw from the country.

There, an ISIS branch, ISIS Khorasan, or ISIS K, is gaining ground and recruiting militants disillusioned with the Taliban's decision to operate as a political entity and not, primarily, as a jihadi one. As the Middle East expert Nicholas Heras of the Center for a New American Security previously told INSIDER, ISIS K is trying to make the case that Afghanistan is the perfect place to wage holy war on a multiplicity of fronts.

"ISIS K will likely succeed," Heras said.

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