President Donald Trump was warned that if he withdrew US troops from northern Syria it could have catastrophic consequences.

Less than a week after Turkey invaded, the nightmare scenario Trump was warned about has become a reality.

ISIS is already regrouping, US credibility has been badly damaged on the global stage, and Russia is the biggest winner of all.

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Almost as soon as the Trump administration abruptly announced it was withdrawing US troops from northeast Syria, alarms were raised across Washington.

Republicans and Democrats alike warned President Donald Trump that on top of abandoning the US-allied Kurds to a potential massacre at the hands of the Turkish military, the move would create a security vacuum in the region that Russia, Syrian President Bashar al-Assad, and ISIS would exploit.

Turkey invaded Syria last Wednesday.

In less than a week, the nightmare scenario Trump was warned about has become a reality.

ISIS is making a comeback

ISIS is already regrouping and has claimed responsibility for at least two attacks in Syria since Turkey invaded.

The Kurds had been guarding roughly 11,000 ISIS fighters, including approximately 2,000 foreign fighters, prior to the Turkish military incursion. But the Turkish assault has diverted their attention, as US forces have also suspended operations against ISIS as the Pentagon announced the US is withdrawing the remaining troops in northern Syria on top of the small group already relocated.

Over the weekend, hundreds of ISIS-related detainees escaped from a prison camp in northern Syria.

Trump suggested the escape may have been the work of the Kurds to bait him back into Syria, but there's no evidence of this and Defense Secretary Mark Esper subsequently blamed Turkey.

"This unacceptable incursion has also undermined the successful multinational 'Defeat ISIS' mission in Syria, and resulted in the release of many dangerous ISIS detainees," Esper said in a statement.

The Turkish military operation is a direct result of Trump's decision to withdraw US forces from northeast Syria and the move — which Trump announced after a phone call with Turkish President Recep Tayyip Erdogan — was widely seen as a greenlight to Erdogan to begin his long-desired assault on the Kurds.

Read more: Trump's coziness with authoritarians is backfiring spectacularly in Syria

The White House has rejected the notion he paved the way for the Turkish operation. But in announcing the abrupt withdrawal of US troops from the region last Sunday, the Trump administration said: "Turkey will soon be moving forward with its long-planned operation into Northern Syria...United States forces, having defeated the ISIS territorial 'Caliphate,' will no longer be in the immediate area."

As Brett McGurk, Trump's former top US envoy for the fight against ISIS, put it in a tweet on Tuesday, "Trump administration officials are working overtime to say he never gave the green light to this disastrous gift to ISIS, Russia, and Iran. I don't envy them. But it's demonstrably false."

"The disaster unfolding tonight in Syria was predictable from the moment Trump made clear he wanted to leave," McGurk said in a separate tweet on Sunday.

Trump handed a big victory to Assad and Putin

Within the first week of the Turkish operation, both the Pentagon and the United Nations have warned there are already signs war crimes have been committed against the Kurds by Turkish-backed Syrian Arab forces.

In this context, and having been abandoned by the US, the Kurds have turned to Damascus and its allies in Moscow for protection against the Turkish assault.

The US moved out, and its adversaries capitalized on it.

"After the Americans abandoned the region and gave the green light for the Turkish attack, we were forced to explore another option, which is talks with Damascus and Moscow to find a way out and thwart these Turkish attacks," senior Kurdish official Badran Jia Kurd said. "This is a preliminary military agreement. The political aspects were not discussed, and these will be discussed at later stages."

Trump seemingly has no problem with this, and has presented the chaos in Syria as a distant problem.

The president on Monday tweeted; "Anyone who wants to assist Syria in protecting the Kurds is good with me, whether it is Russia, China, or Napoleon Bonaparte. I hope they all do great, we are 7,000 miles away!"

Russian troops have now moved into areas abandoned by US forces, in one of the biggest physical indications Moscow is filling the void created by Trump's retreat.

Putin's and Assad's gains in Syria are also beneficial to Iran, which is allied with both and is only separated in geography from Syria by Iraq.

In another clear win for Moscow, the Turkish invasion has raised tensions within NATO as the historic alliance simultaneously works to counter Russian aggression in Europe.

Turkey is a NATO member, and its invasion in Syria has been condemned by the alliance.

British Prime Minister Boris Johnson and NATO Secretary General Jens Stoltenberg both say Turkey's operation needs to end, a spokeswoman for Johnson said on Tuesday after the two met in London. "The Prime Minister and Secretary General both expressed their deep concern at the situation in northern Syria," the spokeswoman said.

Meanwhile, Trump on Monday announced he's sanctioning Turkey over the incursion, further complicating the already convoluted dynamic between the two countries.

In withdrawing from northern Syria, the US abandoned one ally in the hopes of appeasing another. The US partnership with Kurdish forces placed strains on relations between Washington and Ankara.

But if Trump originally hoped to improve relations with Turkey via this move, it's backfired spectacularly as he faces mounting pressure in Congress to punish Erdogan over the Syria operation.

America's credibility is in tatters

Critics of Trump's decision to abandon the Kurds say he's sent a dangerous message to other allies and potential partners that the US cannot be relied upon.

European leaders have slammed the US withdrawal, as they express concerns about new security threats posed by ISIS as well as the escalating humanitarian crisis.

The European Union's foreign policy chief, Federica Mogherini, said the situation could allow ISIS to "re-find its breathing space inside that territory" and poses a direct threat to European security.

Read more: Trump defends abandoning the Kurds by saying they didn't help the US in WWII

Norbert Röttgen, the chairman of the German parliament's foreign affairs committee, told The Washington Post: "In withdrawing US troops from Northern Syria, Trump not only let his Kurdish allies down, he also enabled the Turkish invasion in the first place."

Röttgen added that as a result of Trump's decision, "US credibility has been badly damaged" and "regional stability is now at serious risk."

Similarly, Spanish Foreign Minister Josep Borrell on Monday said that if US troops had not withdrawn from northeast Syria then the Turkish invasion would not have been possible. He added: "The American troop withdrawal was a condition in order to make the attack possible."