As The New York Times’s Charlie Savage has previously explained:
The Logan Act is a 1799 statute that bars private citizens from interfering with diplomatic relations between the United States and foreign governments. It makes it a felony, punishable by a fine or imprisonment of up to three years, if an American citizen, without government authorization, interacts “with any foreign government or any officer or agent thereof, with intent to influence the measures or conduct of any foreign government or of any officer or agent thereof, in relation to any disputes or controversies with the United States, or to defeat the measures of the United States.”
A spokesman for Mr. Kerry declined to comment on Monday on Mr. Trump’s charges of illegality. A statement released by Mr. Kerry’s office said he “stays in touch with his former counterparts around the world just like every previous secretary of state.”
“Like America’s closest allies,” the statement said, “he believes it is important that the nuclear agreement, which took the world years to negotiate, remain effective as countries focus on stability in the region.”
It appears that whether Mr. Kerry violated the law is a matter of legal interpretation.
Since the Iran deal is still in place — as of Monday — Mr. Kerry has not undermined or opposed American foreign policy, said Daniel Rice, a fellow at the Institute for Constitutional Advocacy and Protection at Georgetown University.
“Because the Trump administration has not yet decided to reimpose sanctions on Iran, the existing nuclear deal framework — and not its repudiation — is currently a ‘measure of the United States,’” Mr. Rice said. “By attempting to salvage the deal, Kerry plainly did not intend to ‘defeat’ a measure of the United States.”
But it also depends on exactly what Mr. Kerry said to the foreign officials, said Eric Posner, a law professor at the University of Chicago.
“If he has gone further than merely expressing his opinion, and tried to influence the actions of foreign governments by, for example, making promises on behalf of a future Democratic president or Congress, and these promises are credible, there is an arguable Logan Act violation,” Mr. Posner said.
The legal scholars interviewed by The Times all stressed that the law is a paper tiger that has never been seriously enforced. (Two said it may be unconstitutional.)
Still, the Logan Act has occasionally resurfaced as a political cudgel.
While it’s “perfectly plausible” to argue that Mr. Kerry violated the Logan Act, “it’s been violated hundreds of times” with no repercussions, said Michael McConnell, a law professor at Stanford University.
Accused violators include Henry A. Wallace, the former vice president who lobbied against the Truman Doctrine; Jane Fonda, the actress who traveled to Hanoi during the Vietnam War; the Rev. Jesse L. Jackson, the civil rights activist who visited Cuba during a presidential campaign against Ronald Reagan; and 47 Republican senators who wrote to the government of Iran in 2015 to oppose the nuclear deal before it was struck.
The law resurfaced again last year, when it was revealed that Michael T. Flynn, Mr. Trump’s first national security adviser, had discussed sanctions with the Russian ambassador in late 2016 — before the president’s inauguration.
And Mr. Trump himself may have committed the same offense as Mr. Kerry when, during the 2016 campaign, he invited Russia to hack Hillary Clinton’s emails, said Timothy Zick, a law professor at the College of William and Mary. (The suggestion of a Logan Act violation did emerge at the time.)
But given that there have been no prosecutions under the Logan Act in its history, scholars said it’s hard to predict whether Mr. Kerry would be convicted — even if a case was brought against him.
The Logan Act has “been a dead letter for hundreds of years,” Mr. McConnell said. “Its only function is mischief.”