Lucky for John Kerry that no one has ever been convicted (or even prosecuted since 1852) for violating the 18th-century Logan Act, which bars private diplomacy against US interests. Because what the former secretary of state has been doing to pressure President Trump against withdrawing from the Iran deal sure looks like a textbook violation. The Boston Globe reports that Kerry in recent weeks has engaged in “unusual shadow diplomacy” to “apply pressure on the Trump administration from the outside,” holding meetings and phone calls “below the radar” with Iranian and European leaders. Kerry doesn’t deny the meetings, but claims...