Across eastern Ukraine, Russia’s tiny gains are adding up. It is capitalizing on a series of small advances and throwing significant resources into an emerging summer offensive, one that risks reshaping control over the front lines. Over four days reporting in the villages behind Kostiantynivka and Pokrovsk – two of the most embattled Ukrainian towns in Donetsk region – CNN witnessed the swift change in control of territory. Russian drones were able to penetrate deep into areas Kyiv’s forces once relied upon as oases of calm, and troops struggled to find the personnel and resources to halt a persistent enemy...