I believe they have already done enough to be considered an aggressively expanding state who has comitted acts of war. That said, I am not yet certain that WWIII would have any sort of possible positive effect. I believe our best bet (from a utilitarian perspective) would be waging an economic and diplomatic war against them. Sanctions against Russia since the Ukraine events have had significant negative impacts on their economy, and though Putin has created a cult of personality, that cult will fall when he does. Russia isn't the threat, Putin is. In that sense I believe the best bet would be to stall and delay Russia until his death.

In that regard, I believe sanction wars would be one of our greatest paths. Another would be to greatly expand diplomatic relations with India in order to solidify our influence in the South Asian economy and to solidify a military alliance with an emerging superpower very close to Russia.

I would also say that, theoretically, trying to pull China away from Russia would be ideal, but I don't think anyone is under the impression that is impossible. Therefore our interests would be best served by expanding our economic and diplomatic influence in Southern and South Eastern Asia (probably not Oceania, however, considering the strong Islamic populations aren't that big on "the Great Satan").