On Monday, an eerily familiar scene in the streets of Kiev heralded a dangerous new phase in the Ukraine crisis. Once again, riot police faced angry demonstrators who claimed that the government was betraying their country; once again, blood spilled on the pavement, resulting in at least one death and over 100 injuries. This time, however, the players’ roles had shifted. The ones fighting the government were grenade-wielding members of Svoboda and Right Sector, radical militants who had, until that point, been allied with Kiev. Their target was the democratically elected, Western-leaning government of Petro Poroshenko which is working on...