On Thursday, Russia told the U.S. it "will not tolerate any shelling from the areas where the SDF [Syrian Democratic Forces] are stationed, fire from positions in regions [controlled by the SDF] will be suppressed by all means necessary."

This follows a Sept. 16 Russian air strike against SDF and embedded coalition forces operating near the Islamic State-held city of Deir ez-Zor. The U.S.-led coalition responded to that attack, which wounded a number of SDF personnel, by pledging to "defend" the SDF against further attacks.

This showdown reflects the Russia-Iran-Assad axis effort to push the U.S. out of Syria. While the axis campaign has been escalating on the ground and in the air since the early summer, its underlying urgency is explained by advances the Sunni-Arab rebels in the SDF have made. Russia and its partners know that if those forces secure the Iraq-Syria border region, they will also control the flow of goods and persons across the border. And that would endanger Iran's primary strategic objective in Syria: moving men and materiel from Iran to Syria and then on to Lebanon. Lebanon, after all, is the home of Iran's prime ally, the Lebanese Hezballah.

By threatening the U.S. and the SDF, Putin wants Trump to yield U.S. rebel allies to the axis. It's Vladimir Putin-101: use a calculated application of force to scare his adversaries into retreat.

The U.S. must reject this aggressive overture.

As I've explained, the durable, improved stability of Iraq and Syria requires empowering the various sectarian communities of those nations. But Iran and Assad, and thus also Russia, oppose that agenda. They want a contiguous territory of Khomeinism-supplicant rulers reaching from Tehran to Beirut -- Incidentally, this is why Israel is escalating against the axis -- and know that the Sunni tribes native to the Iraq-Syria border region would obstruct that agenda. In turn, it's no coincidence that the SDF forces the Russians are bombing consist of fighters from those tribes.

It doesn't matter to Russia that those fighters and their moderate Sunni tribes have a blood feud with ISIS. After all, for all its claims of fighting ISIS, Russia has two very different objectives in Syria.

First, a dominant Assad victory that allows Russia to retain its naval access to the Mediterranean and existing trading relationships with his regime. Second, an embarrassing U.S. defeat in Syria that weakens America in the eyes of regional actors, and leaves it unable to check Russia's interests.

So where is this leading?

The map tells the tale.

Note the conflagration of U.S.-supported forces in yellow, axis forces in red, and ISIS forces in grey. Following the line of ISIS-held settlements down the Euphrates river, you'll end up at the Iraqi border town of Al Qa'im. As I've explained, Al Qa'im is the pivot on which U.S. interests in stability or axis interests in imperialism rest. Put simply, if we care about counter-terrorism, we must care about not yielding to the axis. Trump must stand up to Putin here.

Regardless, this situation exemplifies how few shared interests the U.S. and Russia actually have.