While President Biden has been distracted by a climate-change conference and sagging approval at home, President Vladimir Putin is building up Russian forces along the Ukrainian border. The Biden administration must respond to this provocation and do what President Obama didn’t—deter Russian aggression against its Western neighbor—before it’s too late.
Russia’s war against Ukraine started in 2014, when Russian forces invaded, seized the Crimean Peninsula, and occupied the eastern regions of Donetsk and Luhansk. Since then, Russian forces have carried out sporadic attacks against the Ukrainian military—using artillery barrages, drone strikes and infantry incursions. Mr. Putin’s war has claimed the lives of more than 14,000 Ukrainians.