The U.S. government has taken care during the past four months to stay out of the Greek crisis, at least in public. President Barack Obama antagonized many European governments in February, when he warned that “you cannot keep on squeezing countries that are in the midst of depression,” which was widely interpreted as endorsing the new Greek government’s leftist program. Since then, the administration had largely kept its counsel private.

But that changed last week when U.S. Treasury Secretary Jacob Lew, speaking in London...