Why Russia is so eager to put the lid on a US military strike in Syria

The paragraph below is about Tartus, a port in Syria:

“Tartus hosts a Soviet-era naval supply and maintenance base, under a 1971 agreement with Syria, which is still staffed by Russian naval personnel. Tartus is the last Russian military base outside the former Soviet Union, and its only Mediterranean fueling spot, sparing Russia’s warships the trip back to their Black Sea bases through straits in Turkey, a NATO member.” [Wikipedia]