Daniel Hemel and Eric Posner write: President Trump’s former national security adviser, Michael Flynn, acknowledged in court last week that he lied to F.B.I. investigators about his communications with the Russian ambassador to the United States in the run-up to Mr. Trump’s inauguration. While Mr. Flynn pleaded guilty to only one count of making materially false statements, his admissions leave little doubt that he also violated a federal criminal statute known as the Logan Act. Mr. Flynn’s filings further reveal that a “very senior member” of the Trump transition team almost certainly violated the Logan Act, too.

We do not yet know the identity of this “very senior” official. Possibilities include Jared Kushner, who is Mr. Trump’s son-in-law; Mike Pence, vice president-elect at the time; and Mr. Trump himself. Whoever it was, Robert Mueller, the special counsel, can make out a powerful criminal case against that person.

The Logan Act makes it a crime for a United States citizen, “without authority” from the federal government, to communicate with foreign officials in order to “influence the measures or conduct of any foreign government” in a dispute with the United States or “to defeat the measures of the United States.” A conviction can result in a prison sentence of up to three years.

The statute, which has been on the books since the early days of the republic, reflects an important principle. The president is — as the Supreme Court has said time and again — “the sole organ of the nation in its external relations.” If private citizens could hold themselves out as representatives of the United States and work at cross-purposes with the president’s own diplomatic objectives, the president’s ability to conduct foreign relations would be severely hampered.

The statute applies squarely to Mr. Flynn. [Continue reading…]