Next Tuesday marks four years since Russia launched its full-scale invasion of Ukraine by land, sea and air.

Four years after Russia launched its full-scale invasion of its neighbor, hundreds of Ukraine's supporters gathered on the steps of the Lincoln Memorial, transforming the heart of the US capital into a sea of blue and yellow.

Four years of war against Ukraine means four years of learning for Russia’s armed forces. But how much have they actually learned, how much have they actually reformed, and how worried should people be once the Ukraine war does end?