Do you remember in 2012, when former U.S. President Obama publicly gave Syrian President Assad an ultimatum that if Assad gas attacked his own people, that was crossing a “red line”, which would lead to military consequences? In other words, the U. S. would respond with military force.
Assad called Obama’s bluff. Assad tested Obama and continued gas bombing his own people. Obama dithered and did nothing. Hence Obama looked weak. America looked weak and impotent. Russia (led by Putin) then a second rate power, sensing American weakness and non-involvement, moved into the Mideast power vacuum. Russia became a valued ally of Assad and regained its influence in the region after decades of being marginalized.