Secretary of State John Kerry said a number of things Sunday about the letter to leaders of Iran signed by Sen. Tom Cotton (R-Ark.) and 46 other GOP senators. Appearing on CBS's "Face the Nation," Kerry said it was "unprecedented," "directly calculated to interfere," and an "unconstitutional, un-thought-out action."

Directly calculated to interfere? Yes. Un-thought-out? Depends whom you ask. Unprecedented? That's been discussed.

The real, newsworthy charge here is that it was unconstitutional. But was it?

Constitutional scholar Louis Fisher of the nonpartisan Constitution Project says no. "I think members have a right to speak on public policy and constitutional issues," he said in a phone interview with The Fix. "We have a free open dialogue, and people can do it and also exercise poor judgement."

Any errors in the letter were political ones, not Constitutional, Fisher said.

The Constitution mentions a few things relating to treaties and treason. Article II, Section 2, outlines the president's power to make treaties, but notes he or she does so "with the Advice and Consent of the Senate." The Constitution also defines treason as either "levying war" against the U.S. or "adhering to [America's] Enemies, giving them Aid and Comfort."

The Logan Act, which was passed in 1799 and prohibits correspondence with a foreign government over any disputes or controversies without "the authority of the United States," has been floated as a possible law the 47 Republicans broke, but Fisher said it hasn't been used since 1803, and today U.S. citizens often travel abroad and meet with foreign governments. (Remember Dennis Rodman's trip to North Korea last year? Dumb, yes, but not illegal.)

As our own Philip Bump wrote last week about the Logan Act:

But it seems that no one has ever been tried for a violation of the law. "Historically, it has been threatened but never used," (Stanford University professor and former federal judge Michael) McConnell said. "There have been various threats of enforcement over the years, but it's never been enforced." The law has been "frequently violated," he added, "but never enforced."
As written, the law is awfully vague, allowing for a number of possible ways it might be broken. A report from the Congressional Research Service in 2006 recounted the case of the one person who's ever been charged with violating the act: Francis Flournoy, a farmer from Kentucky who wrote a letter in a regional paper in 1803 that advocated a new country west of the Mississippi allied with France. He never faced trial, and the new country -- as you may know -- never came to be.
Nor, McConnell pointed out, are the senators who wrote the letter to Iran likely to be the first punished by the Logan Act. That's because of the constitutional "speech and debate clause," he noted, "which exempts members of Congress from arrest or prosecution for acts done in their official capacity." We noted this last week, when considering the possible charges against Sen. Bob Menendez (D-N.J.). A member of Congress can slander you from the floor of the Senate, and there's nothing you can do about it. "Offhand, I can't think of any reason why this would not fall within that," McConnell said.

The Iran letter was an act of political theater that has won the 47 Republicans some fans and some enemies and angered the Obama administration. And there's a legitimate debate about whether it was unprecedented or a good idea. But there's little indication it ran afoul of the Constitution.