Absent U.S. deterrence, the Iranian hardliners target U.S. interests, hence the newly announced deployment of the USS Abraham Lincoln Carrier Strike Group to the Persian Gulf. With its recent increase in U.S. Navy deployments near Iran, the Trump administration wants to deter the Islamic Republic from threatening maritime traffic in the Strait of Hormuz.

Iran is very much on the move, fomenting terrorism and paramilitary activity in the region. Sen. Marco Rubio, R-Fla., warned recently that America "will not distinguish between attacks from Shia militias in Iraq and the [Islamic Revolutionary Guard Corps] that controls them. Any attack by these groups against U.S. forces will be considered an attack by Iran and responded to accordingly."

But Rubio is only half right here. He is correct that the Guard actively uses Shia militias in Iraq as proxy forces. But he is wrong to suggest that all such Iraqi militias operate under Iranian direction. And that distinction must inform how the U.S. responds to any given threat.

Retired Gen. Mark Hertling and I debated some of the nuances here, but the basic point is that an attack by an Iraqi Shia militia might be but isn't necessarily an attack by Iran.

Consider the organization of Shia cleric Muqtada al-Sadr. Formerly a close ally of Iran, al-Sadr has reinvented himself as an Iraqi nationalist. Aligning with the communists — yes, you read that right — the Sadrists won a huge victory in the May 2018 Iraqi elections. Sadr has earned the ire of the Iranian hardliners by his recentering of Iraqi Shia populism outside of Iranian control. This is not to say that Sadr is determined to attack America (he wants to maintain some dialogue). But an attack by Sadr's militia on the U.S. would be unlikely to be an Iranian plot.

It is also important to note here that the nuances of Iraqi politics mean that even pro-Iranian figures, such as the Badr Organization's Hadi Al-Amiri, would be cautious before targeting the U.S. These leaders are less directly controlled Iranian partners than, say, Lebanese Hezbollah leader Hassan Nasrallah. Of course the U.S. shouldn't ignore attacks by these groups, but they represent Iranian interests in varying degrees. Iraqi prime minister Adi Abdul-Mahdi is the ultimate manifestation of these competing ideologies.

Still other Iraqi Shia militias, such as Asa'ib Ahl al-Haq, Kata'ib Hezbollah, and the Imam Ali Battalions, represent extensions of both Iran's Khomeinist ideology and of the Guard. The Guard uses these groups as cutouts or deniable intermediaries for its dirty work. If these groups were to attack U.S. interests, Iran would be a legitimate target for direct U.S. retaliation — and that's one reason they won't do it without orders from Tehran.