The case revealed how a foreign government was able to harness Washington’s industry of lawyers, lobbyist and public relations experts, an unflattering portrait that included at least four million dollars in secret offshore bank transfers from an oligarch to Mr. Craig’s law firm.

But Mr. Craig’s guilt or innocence turned on a relatively narrow question of whether he deliberately misled Justice Department officials who were investigating whether he should register as a foreign agent because of his interactions with American journalists about his law firm’s work for Ukraine.

The case was viewed as a test of the Justice Department’s new aggressive campaign to enforce a once-obscure foreign lobbying law. Until roughly two years ago, violators of the statute, known as the Foreign Agents Registration Act, or FARA, typically received only an administrative slap on the wrist.