Russia is struggling to breach Ukraine's defenses because its troops keep getting blown up by drones when they gather in groups: ISW

• Russia is struggling to break through Ukraine's defensive lines. 
• When troops gather for a large assault they're targeted by drones, analysts said. 
• The use of drones has been a central part of the war in Ukraine. 

Russia is struggling to break through Ukraine's defensive lines because when its troops gather to attack, they're targeted by Ukrainian drones, a think tank said.