"What has been building up for the Ukrainians is fundamentally a manpower issue," a former senior Pentagon adviser told Newsweek.

Days before the leaders of Russia and the U.S. hold a summit meeting in Alaska, Moscow’s forces breached Ukrainian lines in a series of infiltrations this week in the country’s industrial heartland of Donetsk.

President Trump said that he and Russia's Vladimir Putin made progress in talks to end the war in Ukraine, but the two leaders did not announce any steps toward reaching a ceasefire.