Russia is slowly grinding through the Donbas as Ukraine braces for a brutal fight over its last strongholds

A Ukrainian soldier looks out of a window of an apartment destroyed by shelling in the direction of Kostiantynivka. Alex Nikitenko/Global Images Ukraine via Getty Images Russia is advancing slowly through the Donbas as Ukraine prepares to defend its last major strongholds. Ukrainian commanders say the fight for Kramatorsk and Sloviansk could become brutal battles of attrition. Analysts warn the outcome may hinge on Ukraine's ability to keep troops supplied under relentless drone and air…