Vadimir Putin has his own reasons for backing the Syrian regime, but he's not spelling them out to the world.
Russia's rigidity on Syria has roots in another civil war
What is Vladimir Putin's game plan for Syria? He has been hiding from the world, supposedly forming his new government after his re-election as president. At least, that was the reason he gave for missing the summit of G8 leaders hosted by US President Barack Obama at Camp David in mid-May.
The question is getting more acute as a result of the stalemate over Syria at the UN Security Council, which even the massacre in Houla has not shifted. Russia is staunchly defending its ally, President Bashar Al Assad. But diplomats are asking, for how long, and to what end?
The question was raised with unusual bluntness by Susan Rice, the US ambassador to the UN, who said that the worst and most likely outcome of the current diplomatic paralysis was the conflict spreading and the international community taking action "outside the authority of the Security Council".
It is unusual for diplomats to anticipate the death of an existing process - in this case the six-point peace plan put forward by Kofi Annan, the UN and Arab League envoy to Syria. There is usually a fear that the prophecy will be self-fulfilling, leaving the diplomatic world with no leverage to slow the drift to war.
Ms Rice's remarks were aimed at delivering a jolt to Russia, which is rejecting any UN action against Syria. Action "outside the authority of the Security Council" inevitably recalls the Nato air campaign in 1999 in Kosovo, which forced Russia's ally, Serbia, to withdraw from the province. Since then Kosovo has achieved independence, a painful reminder to the Kremlin of its reduced global reach.
Ms Rice is thus offering the newly re-elected President Putin a choice: either to work in concert with the western powers to bring about an orderly political transition in Syria, or to face the prospect of Nato - or some other group of nations - intervening in Syria, and once again showing the world that Russia's pretensions to global power are hollow.
Mr Putin will hear more of the same argument today, when he visits Germany and France. It is time for him to say how Russia will use its influence on Mr Al Assad in Syria.
Western diplomats have no doubts what should be going on inside Mr Putin's head: they understand that Russia is determined not to allow the Americans to pull the same trick they did over Libya, where a resolution to protect civilians morphed into carte blanche to topple Muammar Qaddafi.
Russia has set down its marker, and will not be duped again. So now it is time for Mr Putin to stop being part of the problem and become part of the solution. This may not happen immediately, but it is the only sensible long-term course.
The Russians are standing by their ally, insisting that any UN action to weaken the regime will create a zone of US-created instability stretching from Libya to Iraq. This argument hardly puts the Kremlin on the right side of history, suggesting as it does that Libya would be better under Col Qaddafi and Egypt more vibrant under Hosni Mubarak.
The first question Mr Putin has to answer will be the one framed by Ms Rice. Does he think that the US will take military action "outside the authority of the Security Council" against the Assad regime? The short answer must be no.
Russia sees Mr Obama as a man uncomfortable using military force (though ambitious in the covert forms of warfare such as drones) who sees foreign adventures as likely to harm his re-election prospects. So the idea of him leading a Nato air campaign in Syria is ruled out, even when being egged on by his Republican rival for the presidency, Mitt Romney. Given the lack of unified Syrian opposition, the chances of this happening look even slighter.
Mr Putin has more to lose from regime change in Damascus than just his pride. Syria provides Russia with its only naval facility on the Mediterranean, at Tartous, as well as a small market for arms exports.
There is also the serious matter of international precedent. Mr Putin used overwhelming force to crush separatism in Chechnya, and may need to do so again. He does not want to encourage a new example of a sovereign state being constrained from using all available means to impose its will. In this he has the strong support of China.
At home, with his rule contested by a middle class that wants more than oligarch-led stability, Mr Putin gains popularity by giving the US a bloody nose over Syria.
The west counters that Russia is not being asked to forego its interests in Syria. If political dialogue led to the departure of Mr Al Assad and his replacement by some other figure from the regime, following the Yemeni example, Russia could keep its naval base. And Mr Putin the peacemaker would be a hero.
But maybe all these western calculations are castles in the air.
If anyone knows what is going on in Damascus, it should be the Russians. Their links with the Soviet-trained intelligence services are deep and broad. When the Russian foreign minister, Sergei Lavrov, visited in February to discuss political dialogue, a prominent member of his delegation was Mikhail Fradkov, the head of foreign intelligence.
With their feelers deep inside the regime, perhaps Mr Putin's old colleagues in the intelligence service understand that the Assad family is determined to stay, and has the tools and resolution to do it.
What if the line in the sand that Mr Putin wants to draw is not about Russia's prestige and role in the Security Council? What if his plan is far grander: halting, at the gates of Damascus, what he sees as the green tide of Sunni Islamism stretching from Morocco, through North Africa and the Levant to Turkey and thence almost to Russia's unstable southern border? If that is the case then to prosecute a civil war in Syria, far from being a disaster, is both necessary and desirable - like the one he fought in Chechnya.
If that is Mr Putin's thinking, then Susan Rice has good reason to be alarmed.
On Twitter @aphilps