"There's an incredibly large force that's on the border," much larger than the one that invaded and annexed Ukraine's Crimean peninsula in 2014, said Philip Breedlove, a retired four-star U.S. Air Force general who was NATO's supreme commander from 2013 to 2016.
"You have a Ukrainian land army that has gotten much better, much more capable," since 2014, said Breedlove, who is now at the Middle East Institute, a Washington-based think tank. "But the Russians would own the air and the sea."