Peter Bergen is CNN’s national security analyst, a vice president at New America and a professor of practice at Arizona State University. His forthcoming paperback is The Cost of Chaos: The Trump Administration and the World. The views expressed in this commentary are his own. View more opinion on CNN.
(CNN)Retired Gen. David Petraeus, who commanded US forces in the Iraq and Afghanistan wars, says the Russians are facing a Ukraine military that is exceptionally determined, surprisingly capable and innovative, and one that is fighting on its home territory for its very survival.