WASHINGTON — When the ancient Greek or Roman playwrights had painted themselves into a corner, plot-wise, they sometimes resorted to the device known as the deus ex machina, in which one of the gods was hoisted over the stage and dropped in to resolve the otherwise inchoate drama.

Something similar happened this week with Syria. The drama had progressed into a mix of international tragedy and domestic political bathos. President Obama’s threat of military action against Syria was right in principle but garnered no real political support — not least because Obama and his generals agree there is no military solution in Syria.

Cue the gods (in Moscow!): The stage directions may have been confusing, starting with a throwaway line from Secretary of State John Kerry followed up quickly by his Russian counterpart. Then suddenly the stage was crowded with a cheering chorus that included U.S., French and Russian presidents, the U.N. secretary-general, the Chinese and even Iranians.

Anyone who thinks this was simply a theatrical accident should go back to drama school. Obama, Kerry and the Russians have been talking about control of Syrian chemical weapons for many months, most recently a week ago at the G-20 meeting in St. Petersburg. Let it be said that the mercurial Vladimir Putin (whom Obama regards as the most transactional leader in the world) knows how to propose an eleventh-hour deal.

The deus ex machina has been cranked into place, but that doesn’t mean the Syria play is over. The complicated diplomatic part is just beginning. I hope Obama and his allies will keep in mind some basic principles, so that we don’t quickly return to another Syria breakdown:

— Obama’s tough line paid off. The Russians endorsed international control of Syria’s chemical weapons only after Obama threatened to attack, and didn’t flinch in St. Petersburg or on Capitol Hill. He may be a weakened president in foreign affairs, but this show of strength regained him some precious credibility. As a Syrian rebel leader told me by phone Monday night, “never go with carrots only.”

— The U.N. Security Council now moves center stage. The right framework is the resolution France was drafting Tuesday, with U.S. help. It would require Syria to place its chemical weapons under international control for supervised demolition. Syria could face military reprisals if it violates this resolution, which the French are proposing under Chapter 7, which authorizes force. Finally, the resolution would call for punishment of those responsible for the Aug. 21 chemical attack. The Russians want to soften this language.

— The next step is revival of peace talks in Geneva, where elements of the regime and the opposition can negotiate a cease-fire and transition plan. The U.S. and Russia, as co-sponsors of these talks, should begin thinking now about how to prevent a chaotic vacuum and sectarian revenge-killing when a political transition begins. The lessons of Iraq and Libya are clear; reconcilable elements of the Syrian army and state institutions must remain intact so they help the rebuilding.

— President Bashar al-Assad must go. The Russians know this; they’ve said so privately repeatedly to U.S. officials. Now they need to make it happen. The U.N. inspectors have gathered evidence that Syrian civilians were killed by sarin nerve gas on Aug. 21; this action could only have been done by the regime. It would be politically dangerous, as well as immoral, to allow Assad to remain in power once these findings are disclosed.

— The U.S. should step up its training and supply of moderate Syrian rebels — less to topple Assad than to provide a counterweight to jihadists in the opposition and help stabilize a future Syria. The first CIA-trained commandos are now heading into the field, in units of 30 or 40. Step up that flow!

— Iran should prove that it deserves a seat at the Geneva table. It can’t be part of the Syria solution unless it changes its destabilizing policies — not just in backing Assad but in its nuclear program, its support for Hezbollah and other actions. A new Iranian president and foreign minister will be in New York in two weeks. The Iranians and the Obama administration should think big about a new security framework for the region.

— Given America’s profound reluctance to fight another war in the Middle East, Israel knows it will have to take responsibility for its own security, including any military action against Iran. The good news is that Israeli power is robust and credible. Both Assad and the Iranians seem to be deterred from reckless action, and the Russians (in secret) are cooperative. Credible threats of force prevent wars.

David Ignatius is a Washington Post columnist. His email address is davidignatius@washpost.com