Syrians dig through the debris of a building as they search for survivors. (Zein Al Rifai/Agence France-Presse via Getty Images)

PRESIDENT TRUMP’S latest defense of Russian leader Vladi­mir Putin included — along with a bow to his denials of meddling in the U.S. election — an appeal to pragmatism. “Having a good relationship with Russia is a good thing, not a bad thing,” he tweeted, adding that “Russia can greatly help” with problems such as North Korea, Syria, Ukraine and terrorism. In theory, that’s true. The problem is that Mr. Putin consistently disregards the deals he strikes with the United States and allied governments. He promises cooperation while in practice seeking to block U.S. objectives and demoralize and divide Western democracies.

Secretary of State Rex Tillerson, who knows Mr. Putin well, ought to be familiar with this duplicity. He nevertheless has been assiduously pursuing deals with the Kremlin. On Saturday, the State Department announced a new bargain with Moscow about Syria that commits Russia to the withdrawal of Iranian forces from the country and to a U.N. peace process ending in internationally supervised elections for a new government. Like the multiple accords about Syria struck with Russia by Mr. Tillerson’s predecessor, John F. Kerry, it sounds too good to be true. Most likely, like all those previous deals, it is.

The agreement is a follow-on from a “de-escalation zone” in southwest Syria brokered by the United States and Jordan with Russia in July. That pact has reduced bloodshed between forces loyal to the Syria regime of Bashar al-Assad and rebels who control substantial territories near Syria’s borders with Jordan and Israel. The new deal calls for “the reduction, and ultimate elimination, of foreign forces and foreign fighters from the area.” That would cover Lebanese Hezbollah units, Iranian troops and Shiite militias that Tehran has imported from Iraq and Afghanistan.

Israel, which objected to the first cease-fire , is not happy with the new iteration. Its officials are saying undisclosed terms require Hezbollah and other Iranian forces to pull back from the sensitive frontier on the Golan Heights, but in some areas to only three miles from Israeli positions. There is no timetable for their full withdrawal from Syria. On Monday, Prime Minister Benjamin Netanyahu made clear that Israel is not bound by the agreement and will continue its own operations, which have included more than 100 strikes against Hezbollah and other Iran-linked targets.

When senior U.S. officials briefing reporters were asked how Russia would compel an Iranian pullout, or oblige the Assad regime to accept fair elections, their only response was to point back to the agreement. It was an unintended echo of Mr. Kerry, who tirelessly argued that Russia had to be tested on its commitments in Syria. When Russia would violate those commitments, Mr. Kerry would insist that Moscow be given another chance.

Mr. Tillerson and the Trump administration stand at the threshold of the same cycle. U.S. officials reckon they have some leverage, in the refusal of Western and allied Arab governments to provide reconstruction aid to Syria unless the U.N. peace process moves forward. Mr. Putin must also weigh the risk that a failure to prevent Iran’s entrenchment in Syria will trigger a potentially devastating war between Iran’s proxies and Israel. Still, Mr. Tillerson ought to avoid the foolish error of Mr. Trump: assuming that Mr. Putin, in offering improbable assurances, “means it.”