The Source You Cannot Name
A journalist publishes an investigation revealing systematic corruption in a government agency. The investigation is based, in significant part, on documents and testimony provided by a person inside the agency who wishes to remain anonymous. The government demands that the journalist reveal the source. The journalist refuses.
This is not a difficult case. It is the definitional case. If the journalist reveals the source, the source faces retaliation. If the source faces retaliation, no future source will come forward. If no future source comes forward, the next corruption goes unreported. The chain is direct, predictable, and well-documented.