VENICE — What do Supreme Court justices do on their summer vacations? For Justice Ruth Bader Ginsburg — longtime liberal standard-bearer, recent Donald J. Trump critic — this year’s answer is: Go to Venice, watch your grandson perform in a production of “The Merchant of Venice” and preside over a mock appeal of the city’s most notorious resident, Shylock.

And so, on Wednesday afternoon, in the monumental 16th-century Scuola Grande di San Rocco, beneath ceiling paintings by Tintoretto, Justice Ginsburg and four other judges, including the United States ambassador to Italy, John R. Phillips, heard arguments on behalf of Shylock and two other characters, before reaching a unanimous ruling.

“I’d describe it as fun,” Justice Ginsburg said of the coming mock appeal in an interview on Tuesday, in which she talked about Venice, which she first visited on her honeymoon in 1954, and Shakespeare, whose work she loves — but not about Mr. Trump, weeks after she said she regretted her remarks criticizing the man who is now the Republican presidential nominee.

The mock appeal began where the play ended: Shylock, the conniving Venetian Jewish moneylender, insists on collecting a pound of flesh from Antonio, who has defaulted on a loan. But a lawyer, actually Portia disguised as a man, finds Shylock guilty of conspiring against Antonio and rules that he must hand over half his property to Antonio and the other half to the state.