Marked success in stabilizing Mr. Assad with little cost appears to have fed larger goals. Once the agreement with Washington fell apart, Mr. Putin went all out to win Aleppo for Mr. Assad, no matter the price on the ground, to help Damascus gain control over some swaths of western Syria that would then force the opposition into an agreement.

“Russia has a window of opportunity to do it,” said Nikolai V. Petrov, a Russian professor of political science, said. “The next American president will face a new reality and will be forced to accept it.”

Various potholes mar the route to long-term success, however, one reason Russia rapidly agreed to new negotiations over Syria. For example, some unusual public grumbling has surfaced from the Russian military that the Syrian Army is an unworthy ally.

“The Syrian armed forces have not conducted a single successful offensive during the past year,” wrote Mikhail Khodarenok, a retired colonel and respected military analyst on Gazeta.ru, a Russian news website. The article included a scathing assessment of corruption and general fecklessness throughout Mr. Assad’s military, and it called militia allies from Iran and Hezbollah equally suspect.

Beyond Syria, Mr. Putin harbors ambitions of restructuring the global order, with an eye to restoring Russia to what he sees as its rightful status in the upper tier.

“I believe that the talk about looming war is a propaganda trick: Russia wants to show that it can go far, it is an element of pressure,” said Aleksei Makarkin, the deputy head of the Center for Political Technologies, a Moscow think tank. “Russia dreams about another Yalta conference, where together with other great powers it will divide the map.”

Mr. Putin himself said as much in remarks on Wednesday: “Let us not forget that we bear a special responsibility as the two largest nuclear powers for maintaining international peace and security at the global level.”