Russia is the nation having the largest number of nuclear weapons. In addition to that, they have the most powerful inter-continental ballistic missile in their possession. Only retards will go for a war against Russia.
Don't be too sure about that. Close to 2,000 Russian servicemen are stationed in Syria. In case the Americans target any of these military bases, killing large number of soldiers, then Russia will definitely retaliate (although I can't predict the scale of the retaliation right now).