On Sunday, Russia entered the third month of its invasion of Ukraine, with no sign of an end in sight. Despite severe pushback in the shape of the toughest economic sanctions ever imposed on a country, the ruble, the Russian currency, appears to be strengthening.What’s become evident is that, despite an enormously broad package of sanctions on Russia’s government and oligarchs, as well as an exodus of foreign enterprises, the moves are mostly ineffectual if foreign nationals continue to consume Russian oil and natural gas, which supports the ruble.On Feb. 24, the first day of the invasion, the ruble traded...