Why did Russia announce Syria withdrawal now?

Former senior IDF official tells 'Post' that Putin's announcement to pull forces from embattled Syria "should not be taken at face value."

Russian war planes leave Syria for Russia
Russian President Vladimir Putin’s announcement to withdraw forces from Syria “should not be taken at face value,” a former senior IDF official said Tuesday.
“We should remember the difference between declarations and operations,” said Gen. (res.) Assaf Orion, who until last year was the head of the strategic division in the IDF General Staff and is now a senior research fellow at The Institute for National Security Studies.
The basic question, he said in an interview with The Jerusalem Post, “is not why Russia is pulling out, but why was it declared now.”
“I usually recommend comparing words with deeds, so let’s wait and see what leaves and what stays behind,” he said, adding that Russia may well keep a significant force in the country.
Russia has already indicated that the advanced S-400 air-defense system would stay in Syria, and Orion expects that air force and naval assets also will be left behind.
The Middle East expert suggested that explanations might be found in other theaters, as well as in Russia’s domestic considerations and interests.
An interesting point, he continued, is that “since president Putin never declared publicly the exact goals of the Russian mission in Syria, he can now elegantly state that they were achieved and officially terminate it [the mission] while preserving the flexible options he needs.”
The Syrian campaign has cost Russia $700 million-$800m., according to a Reuters estimate, and cost saving is seen by some as a possible motivation at a time of low oil prices.
Daniel (Dima) Course, a founding member of the Israeli Center for Russian and Eurasian Studies who also teaches at Ariel University, told the Post “the decision [to withdraw] surprised everyone outside, and even inside, Russia.”
It even appears that Putin made the decision alone or only with a few close advisers, Course asserted.
Regarding the financial factor, Course does not see it as critical since the country is enhancing regular military exercises all across Russia at a higher cost than its Syrian involvement.
Therefore, the Russian expert concludes that there are several likely reasons at play such as to pressure Syrian President Bashar Assad to make concessions or because of disagreements with Iran such as its demand to change conditions in some commercial contracts.
In addition, Course sees Russia as trying to repair relations with Sunni states such as Saudi Arabia.
Lastly, he asserted that Russia may have wanted to avoid bad scenarios such as a Turkish intervention in Syria and “as the stakes became high, maybe Putin decided to get out and win some points.”
Lt.-Col. (Res.) Moshe Marzuk, a researcher at the Institute for Counter- Terrorism at the Interdisciplinary Center Herzliya’s Institute for Policy and Strategy, told the Post the Russians “won’t leave completely because they have continued interests there.”
The Russian military intervention came when its interests were at risk in the country, he said, and now that it has strengthened Assad, the regime can negotiate from a position of power.
“Putin came to the conclusion that the political process couldn’t advance without an agreement from all sides,” including the Saudis and the Turks.
If Russia follows through on the declaration to withdraw a significant amount of forces, Marzuk expects Hezbollah to follow suit since it faces internal Lebanese pressure, in addition to Saudi Arabia’s actions against the Shi’ite group and its cutting off of aid to Lebanon.