Earlier this week, Iran seized a Marshall Islands-flagged ship as it passed through the Strait of Hormuz — ostensibly for “legal” reasons related to a decade-old spat between the Danish shipping company, Maersk Line, and Tehran. However, as Patrick noted at the time, the action has all the telltale signs of an attempt by Iran to test the limits of its power to restrict navigation in nearby waters. The ship, Maersk Tigris, was after all technically under the protection of the United States: “The United States has full authority and responsibility for security and defense of the Marshall Islands,” according to the Amended Compact of Free Association that the U.S. and the Marshall Islands negotiated in 2004.

Perhaps unsurprisingly, within hours the Pentagon determined that the U.S. had no such responsibility. But now comes this, via Fox News:

U.S. Navy ships will begin to accompany U.S.- and British-flagged commercial ships as they travel the Strait of Hormuz, a defense official confirmed to Fox News, on the heels of Iran seizing a cargo ship. . . .
When asked how long the U.S. Navy planned to accompany U.S. flagged ships through the strait, [U.S.N. 5th Fleet spokesman Commander Kevin] Stephens said “we don’t have an end date in mind.”
He said Secretary of Defense Ash Carter signed off on the order, which came at the recommendation of U.S. Central Command, responsible for the Persian Gulf and surrounding area. The Navy had discussed the idea of with shipping companies and “they all wanted the support,” said Stephens. . . .
When pressed on what kind of incident aboard the ship would elicit a U.S. Navy response, he was vague, saying: “These [U.S. military] assets give commanders options.” He said he didn’t know “what the possibilities are,” and the U.S. government is “in discussions with the Marshall Islands on the way ahead.”

Yet another example of the current administration’s schizophrenia. Iran is pressing its regional power, knowing that the United States is unlikely to push back, because its current commander-in-chief is desperate for a nuclear arms deal. He, unlike his negotiating partners, is unwilling to rock the boat. Yet the Defense Department — whatever Pentagon lawyers might have said – is (quietly) not of the opinion that Iran was merely exercising a legal prerogative. Rather, it thinks (rightly) that Tehran was flexing geopolitical muscle. Consequently Secretary Carter has approved flexing a bit of U.S. naval muscle to ward off Iranian overreach.

The question, then, must be: Precisely where does the “red line” fall for Iranian aggression?

Jay has expressed this concern about Putin and NATO:

My worry is, if Russia aggressed against a Baltic nation — a NATO member — neither we nor NATO at large would lift a finger. And the appetite for conquest would grow.

That is equally true in the Persian Gulf — and the aggressor there may be even more dangerous.