Russia is bolstering Assad with grain from Crimea:
Crimea has stepped up grain exports to Syria over the past year in an arrangement that gives the Black Sea peninsula an outlet for its surplus crops and ensures President Bashar al-Assad has a reliable source of wheat.
Shipments started picking up in the middle of last year and at least 10 ships took a minimum of 170,000 tonnes of grain to Syria between July 2017 and May 2018, according to port and ship tracking data seen by Reuters and confirmed by shipping sources.
The recent rise in grain shipments from Crimea is helping to support Assad's government, as a steady supply of wheat is critical to providing the heavily subsidized bread that many Syrians depend on.
This line of supply reflects the reality that control of Crimea allows Russia to project power into the eastern Mediterranean Sea to support their bases in Syria:
I've noted that Russian intervention in Syria might not have been justified without Russia's conquest of Crimea. Crimea makes the most sense as a Russian base to project power into the eastern Mediterranean Sea to extend Russia's defensive perimeter to that region. And Syria is the most likely place for Russia to base forces near that area (unless Russia completely flips Turkey or Greece).
It is quite possible that the Russian invasion of Ukraine led to the Russian intervention to save Assad.
But I digress.
Of course, Russia needs to have Turkey on their side to secure the line of supply and communication through the Turkish straits. Will Turkey align with Russia despite the long history of warfare?
The weight of history argues against such an alignment for long. But in the short run, which could last decades, the lack of a common land border makes it easier for Turkey to work with Russia.
