When President Barack Obama visited Berlin in June, German Chancellor Angela Merkel made a point of showing him a balcony in her office overlooking train tracks that crossed the border of her once-divided country — a symbol of her upbringing on the east side of the divide, where eavesdropping by secret police was rampant during the Cold War.

The private moment between the two leaders underscores the degree to which Merkel’s personal history has influenced her outrage over revelations that the National Security Agency was monitoring her communications. The secret spying threatens to damage the close relationship between Obama and Merkel, which, until now, has been defined by candor and trust.