This jolting question is raised by Graham Allison and Dimitri Simes in the cover article of The National Interest.

The answer the authors give, in "Countdown to War: The Coming U.S. Russia Conflict," is that the odds are shortening on a military collision between the world's largest nuclear powers.

The cockpit of the conflict, should it come, will be Ukraine.

What makes the article timely is the report that Canada will be sending 200 soldiers to western Ukraine to join 800 Americans and 75 Brits on a yearlong assignment to train the Ukrainian army.

And train that army to fight whom? Pro-Russian rebels in Ukraine whom Vladimir Putin has said will not be crushed, even if it requires Russian intervention. Says Putin, "We won't let it happen."

What are the forces that have us "stumbling to war"?

On our side there is President Obama who "enjoys attempting to humiliate Putin" and "repeatedly includes Russia in his list of current scourges alongside the Islamic State and Ebola."