Recall when McCain wanted to go into Syria guns ablazin. Obama put the brakes on that to a degree and he did allow Putin to have at it.
Russia accelerated their air campaign in Syria, Obama also deported several Russia spy houses over election interference.
When Trump 'took over the US' policy became more confused but still maintained a presence in Syria in cooperation with Russia to not attack their planes. I have lost track about what we are doing there today.