When US Secretary of State Rex Tillerson visits Moscow this week, the stakes could not be higher. If Washington and the Kremlin are not able to come to a meeting of the minds on Syria, it could set the two powers on a collision course.

The expansive way in which US officials have talked about the purpose of last Friday's limited US strikes in Syria increases the prospects of mission creep. The broader the US Administration's goals in Syria, the more prone it will be to pressure to escalate there. Already, some regional allies have called for more forceful action. And congressional hawks are urging President Donald Trump to provide Syrian opposition groups with more weapons, impose a no-fly zone, and conduct further airstrikes in order to pressure Russia and Bashar al-Assad to agree to a political settlement. As Assad continues to kill civilians, the calls for deeper US involvement aimed at ousting him will mount.

If the US goes down this road, the prospects of a military confrontation with Moscow are real. Russian military personnel are distributed across Syria's key military bases. Moscow has air defence systems in Syria, and Russian planes police Syrian skies. An extensive US campaign would run big risks of killing Russian troops.

Russia and the Assad regime are likely to respond by reorienting their air defence network toward US and coalition aircraft fighting Isis, or by attacking areas where US troops are.


Even if the Trump Administration sticks to deterring further chemical attacks, successful deterrence requires a credible threat.

Assad may attempt to test Trump. And Trump, having invested his personal credibility in standing firm, may find himself psychologically or politically compelled to respond, despite the very real risks that it could result in a direct military clash with Russia.