How much will Europeans sacrifice to save Ukraine?

Western solidarity with Ukraine will last as long as public sympathy holds. Vladimir Putin is betting democracies cannot withstand hardship. Can Europe and the U.S. prove him wrong?

It feels jarring – almost disrespectful – to write these words as civilian corpses are cleared from the streets of Bucha, Ukraine, after Russian troops retreated from the Kyiv suburb. But Ukraine’s fate may well now hinge on a crude question of international politics.

It is this: How long can Washington and its European partners – governments and citizens – maintain their...