With one single tweet, Trump has destroyed US policy in the Middle East
With his decision to withdraw all US forces from Syria, President Donald Trump hands a huge New Year's gift to President Bashar Assad, Isil, the Kremlin and Tehran.
He also guarantees the reversal of US military gains there and extinguishes any leverage Secretary of State Mike Pompeo and his special envoy for Syria, James Jeffrey, may have to drive a diplomatic settlement that meets the administration's own goals of keeping Isil and Iran out.
Most important, Trump falls into the same trap President Barack Obama did when he withdrew all US forces from Iraq in 2011.
He virtually ensures security will disintegrate further, that Isil and Iran will surge again, and that the US will be compelled to come back into Syria at even greater military cost and in more adverse conditions than if it had stayed.
Everything about this mercurial decision imperils US national interests as defined by Mr Trump himself.
First, Isil is far from gone in Syria. Just six months ago, the Pentagon estimated 20,000 to 30,000 fighters remain active in Syria and Iraq.
Isil may no longer control vast swathes of Syria, but its fighters are hiding in ungoverned pockets in the east and in the back alleys of Idlib.
As soon as the US withdraws, Isil will make three moves.
It will claim victory over the US infidels, turbocharging a recruiting binge across the Middle East and South Asia.
It will pour fresh fighters into eastern Syria. And it will come out of the shadows to retake territory across eastern Syria from the Syrian Democratic Forces (SDF), which cannot hold Raqqa or any other cleared territory without continued US help.
Iran will also flood the zone the US is abandoning. Tehran has likely already given orders for Hezbollah militias it controls to turn east.
Just three months ago, national security adviser John Bolton pledged that the US would stay in Syria until the last Iranian fighter had been driven out.
With one tweet, Mr Trump has instead invited Tehran to deepen its military, political and economic grip.
In the process, Iran will gain control of major oil fields in Deir al-Zour protected by US forces and the SDF, allowing it to self-finance its land grab.
Moscow is celebrating, too. After years of pretending to negotiate a diplomatic solution to the Syrian crisis with Washington, Vladimir Putin can now ignore the entreaties of Mr Trump's envoys because the US will have no military skin in the game.
The Kremlin will proceed as it has long planned, consolidating control over the rest of Syria for Assad until 2021 and then rigging an election for a new figurehead.
Moscow will be too smart to expand its own ground presence in Syria, and will instead broaden its tacit support for the Iran-backed militias that are already serving as de facto local police forces in western Syria.
Maybe it will allow Tehran to split the spoils from the Deir al-Zour oil fields; maybe all that cash will go to Moscow instead.
Of course, both Isil and the beleaguered SDF will fight for that territory, too, setting off another cycle of bloodshed and Iranian weapons shipments into Syria.
US diplomacy also died another sad death with Mr Trump's tweet.
A few thousand tweets ago, the president criticised his predecessor for leaving Iraq to Isil in 2011, then having to return in force in 2014.
The United States currently has 5,200 troops deployed to Iraq and spends $13.6m every day on military operations there.
By that measure, the president should consider the 2,000 troops in Syria a bargain, an insurance policy and vital leverage against far worse outcomes for the US, for Syria and for the global balance of power. (©The Washington Post)