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While Washington was watching impeachment proceedings, a humanitarian disaster brewed in Syria. The crisis in Idlib, which threatens to be among the worst in a nine-year-long war full of them, is a reminder that the Syrian war hasn’t gone away — and that it has the capacity to worsen.

Idlib, which lies in northwest Syria on the Turkish border, contains the last rebel-held territory in the country, and Syrian President Bashar al-Assad has been trying to take it by sheer and brutal force.

Turkey, a backer of rebels who oppose Assad, stands opposed. In recent days, that tension has boiled over into violence. Turkey’s defense ministry said Monday that seven Turkish soldiers and one Turkish civilian were killed in Idlib by Syrian army shelling.

In response, Turkish forces launched an operation that it said “neutralized” 76 Syrian soldiers. On Wednesday, Turkish President Recep Tayyip Erdogan warned of further action if Syrian troops did not retreat from Turkish observation posts in Idlib.

If not, “Turkey will have to take over the matter,” Erdogan told the parliament in Ankara. Most analysts think that “Turkey and Syria are effectively in a state of undeclared war today,” Al Monitor’s Semih Idiz wrote.

An outright Turkish-Syrian conflict would be a geopolitical mess. Syria’s Assad is allied with Iran and its offensive in Idlib has the backing of Russian air power, putting Erdogan’s own relationship with Tehran and Moscow under strain.

Then there’s another inconvenient truth: Turkey is a U.S. ally housing an estimated 50 U.S. nuclear bombs about 250 miles from the Syrian border. It is also a NATO member, meaning the United States, Canada and much of Europe have pledged to protect it from aggression.

But the biggest impact so far is on Idlib’s civilians, including many women and children. The Syrian war has dragged on for almost a decade with atrocities and mass exoduses, but by any standard this escape from Idlib ranks highly.

Rights groups say that at least 150,000 people have fled their homes in the past two weeks, bringing the total of those displaced since Dec. 1 to more than 500,000. Videos from the scene show chaotic traffic jams to escape areas close to the bombing.

The desperation to leave is understandable. Throughout the war, Syrian forces and their Russian backers have purposely hit civilian infrastructure in the push to take Idlib. In a statement, Michelle Nunn, president and chief executive of Care USA, said that there were 85 attacks on health-care facilities in northern Syria in 2019, and that so far in 2020 that trend was continuing.

“In the past two months, close to 300 civilians have been killed as a result of the intensifying hostilities in northwest Syria,” David Miliband, CEO of the International Rescue Committee, said. “If this violence continues, up to 800,000 people currently in the firing line will be left with few options for safety.”

Investigations have proved that Russian airstrikes deliberately targeted Syrian hospitals last year. But there may be little recourse: Bloomberg News reported this week that Moscow had been able to use its clout at the United Nations to stymie the investigation of human rights abuses in Syria.

Still, foreign governments ought to pay close attention to Idlib. The world has seen the global effect humanitarian disaster in Syria can have. More than 5.6 million refugees have fled the country since the war began. Turkey is home to millions of them — and it hopes for less, not more.

“Turkey’s presence in northern Syria is the only barrier against yet another humanitarian crisis,” Fahrettin Altun, communications director for the Turkish government, wrote on Twitter this week. “Our western allies have allowed this crisis to fester for too long. They only pay attention when they are threatened by the influx of refugees.”

For many, the best option may be tentative support of Ankara. Secretary of State Mike Pompeo issued a statement this week saying the United States stands behind Turkey and noting its status as a NATO ally.

But Turkey and the United States have a deeply damaged military relationship. It was only a few months ago that the United States was condemning Turkey for its moves into Syria against Kurdish forces. Reuters reported on Wednesday that the United States halted a secretive military intelligence program with Turkey in October after the incursion.

That incursion took place after President Trump unexpectedly announced that U.S. troops would be leaving Syria. Though that promise has, in effect, not been kept, Syria is not high on the administration’s list of priorities: In the president’s State of the Union speech on Tuesday, it was only mentioned in reference to the slain Islamic State commander Abu Bakr al-Baghdadi.

Trump had hoped to wash his hands of Syria. But Idlib’s crisis suggests that it won’t be that easy.