demands. it fail discuss nato troops in the region. that's been a nonstarter. they did offer a diplomatic path out of the crisis. and here in the eastern ukraine on the front lines. >> reporter: we are back in the trenches in far eastern ukraine. and you could see in some places they are very narrow but they extend for miles. ukrainian. troops are bracing for the worst. the soldiers say they're ready for anything as the prospect of a russian invasion appears to be increasing. russia's military build up is accelerating. disguised, u.s. officials say, by military exercises in the black sea. these firing drills in the baltic sea and along three sides of the ukrainian border, including these forces in new satellite images. >> and joining me now the former u.s. ambassador to ukraine, peter baker the "the new york