One of the biggest achievements of President-elect Donald Trump's first term in office was the near-complete defeat of the Islamic State terror group and the destruction of its would-be "caliphate" across parts of Syria and Iraq.

Unfortunately, Trump may have to battle the Islamic State again in his second term as the terror group has been resurgent amid the chaos in Syria following the ousting of the Assad regime by Islamist rebels, Fox News reported.

The situation will likely prove more complicated this time around, however, as the rebel groups that defeated Assad are backed and directed by Turkey, a NATO member and nominal U.S. ally, which has its sights set on conquering the Kurdish fighters in Northern Syria that the U.S. is also closely allied with in the fight against the Islamic State remnants.

Fears grow of a resurgent Islamic State group in Syria

Concerns of a resurgent Islamic State in Syria have grown exponentially over the past few weeks following the fall of the Assad regime, particularly now that the main rebel forces backed by Turkey -- radical Islamist Al-Qaeda offshoot Hay’at Tahrir al-Sham (HTS) and the Syrian National Army (SNA) -- have begun to shift their attention toward the U.S.-aligned and predominately Kurdish Syrian Democratic Forces (SDF), which has helped keep the Islamic State remnants in check.

Arguably the biggest worry is that, with the SDF preoccupied with defending itself against Turkish-backed attacks from HTS and SNA, or worse in retreat, thousands of imprisoned Islamic State fighters will escape or be released and join with their holdout jihadist comrades to reconstitute the regional and global threat they presented less than a decade ago.

According to The Washington Post, the complicated situation presents a unique dilemma for the incoming Trump administration and raises the question of how best to utilize, if at all, the roughly 2,000 U.S. troops deployed to Eastern Syria -- plus around 2,500 in neighboring Iraq -- to assist the Kurds in battling the Islamic State while countering Iran's influence.

President-elect Trump has been clear that he has no desire to get the U.S. involved in more conflicts, and he even unsuccessfully attempted to withdraw all U.S. troops from Syria during his first term, but the reality on the ground in that war-torn nation may compel him to not only keep U.S. forces engaged in the area but perhaps even to escalate their level of involvement in the fighting.

Top Biden aide says "resurgence" of Islamic State is the "biggest concern" in Syria

During a recent CNN interview, President Joe Biden's National Security Adviser Jake Sullivan, when asked about the situation in Syria, replied, "The single biggest concern I have is the resurgence of ISIS."

"ISIS loves vacuums," he continued. "And what we see in Syria right now are areas that are basically ungoverned because of the fall of the Assad regime, and ISIS is doing everything it can to try and take advantage of those, to regrow its capability, to threaten Europe, threaten the United States, threaten Americans all over the world."

"So, for example, if Turkey attacks the Kurds -- the Kurds are our best partner to fight ISIS. They would be distracted from that fight," Sullivan said. "The Kurds are the ones who are guarding the prisons where there are thousands of ISIS fighters and tens of thousands of ISIS radicalized family members currently being held in detention. If all those folks got out, you'd be talking about a serious threat to the United States and our friends."

He added, "So our goal is to ensure that we support the SDF, the Kurds, and that we keep ISIS in check. And that's why President Biden, right after Assad fell, ordered airstrikes against ISIS positions, because we are determined not to let them reestablish the kind of position they had 10 years ago."

Incoming Trump advisor says keeping Islamic State down will be a "top priority"

According to Al-Monitor, Trump's incoming NSA, Rep. Mike Waltz (R-FL), said in a recent interview that preventing the Islamic State from reconstituting its former threat would be a "top priority" for the next administration, and noted, "Tens of thousands of fighters and families that are sitting in prison camps guarded by our friends the Kurds, supported by us, and we can’t have that unleash again. That's our key interest."

The congressman added of President-elect Trump, "His mandate overwhelmingly was do not drag us into Middle Eastern wars. We do not need American boots running around Syria in any shape or form. But we are keeping an eye on those things."

The Post reported that Waltz said similarly in a recent Fox News interview, "The president has been crystal clear on his mandate from the voters was to do everything he can to avoid us getting into more Middle East wars," yet added, "But in Syria, he is clear-eyed about the threat of ISIS that’s still there. … We have to keep a lid on it."