Monday’s injury of an American GI and the death of one of our military contractors working with American forces at the heart of Iraqi Kurdistan should be seen as an early Iranian test of President Biden.

The American president’s first, and cautious, reaction is disappointing. It indicates the attack won’t trigger a reevaluation of Mr. Biden’s dash to re-sign a hapless nuclear deal that ignores Tehran’s malign regional activity.

Following the attack on the American-protected airport at Erbil, the capital of Iraq’s Kurdish region, the Biden administration tiptoed around the whodunit. After expressing “outrage,” Secretary of State Blinken said in a statement that America will support the Iraqi government in “all efforts to investigate and hold accountable those responsible.”

Investigate? From Baghdad? America has 2,500 troops left in Iraq, many of them in the northern, Kurdish region. They know full well who was responsible.

A previously unknown group, Awliya al Dam, or Guardian of the Blood, boasted about it. In an eight-point communique, the group vowed it would prevent peace and stability as long as America “occupies” Erbil.

And not only America. The “agent government of the occupiers” would not be spared punishment either, according to the communique. That’s a threat to the elected Barazani government that rules the autonomous region and that recently expressed support for America maintaining a presence in Iraq.

Expressing “brotherhood” with the Kurds, Awliya al Dam nevertheless warns them to stay away from “American, Turkish and Israeli occupation” bases in the region. It threatens to use rockets it stores in the Erbil area to launch “further attacks” until America is expelled from all Iraqi land.

And then comes the tell-tale signoff: “Peace to the blood of the martyrs, peace to Abu Mahdi al Muhandis, peace to Qassem Soleimani.”

Muhandis was Iraq’s leading Tehran-backed operator in the country. General Soleimani, his Iranian controller, commanded the arm of the Iranian Revolutionary Guard Corps’ responsible for exporting its brand of Islamist zealotry to the region and beyond. He was the mastermind behind the vast network of Iran-backed Hezbollah-like militias.

Muhandis and Soleimani had long topped America’s list of most wanted terrorists. After January 3, 2020, when an American drone finally killed them, Tehran and its affiliated regional militias vowed revenge.

“The Guardians of the Blood, obviously, is an offshoot of an Iranian militia,” says Entifadh Qanbar, a Washington-based Iraqi activist. An Israeli intelligence source confirms the attack was likely launched by Hezbollah Iraq, a faction of Hashd al Shaabi, or the Popular Mobilization Force, a coalition of 40 mostly-Shiite militias formed in 2014 to fight ISIS.

That this is a test of Mr. Biden is widely perceived among savviest newspapers; the Wall Street Journal marked the point in an editorial issued today. It suggested that the “world is watching” how Mr. Biden responds on an attack on American forces.

“We dealt with this all the time,” Secretary of State Mike Pompeo told Fox News Tuesday. “Every time the Iranians took action, whether in Iraq or Syria, we imposed full cost on the regime. We first of all called them out. We called it for what it was, an Iranian-sponsored militia inside of Iraq.”

The Biden administration needs to do the same, Mr. Pompeo added. “Just because you’re trying to cut a deal,” he said, “you can’t look away from the kinds of things that put American lives at risk.”

In reality, President Trump signaling endlessly that leaving Iraq (and Afghanistan) was one of his top priorities may have emboldened Iraqi militias as well. But 2,500 Yank troops remain in the country. As long as they’re there the commander in chief is responsible for them and for America’s Iraqi allies.

There may be a worthwhile debate about the wisdom of continuing presence in the region, but Mr. Pompeo’s larger warning, about sacrificing all to attain a deal with the Islamic Republic, is of paramount importance.

The Biden administration is signaling that a return to the deal is imminent. Mr. Biden’s Iran point man, Robert Malley, this week contacted counterparts in Beijing, a close Tehran ally. Mr. Malley also talked to diplomats of other deal partners in London, Paris, Berlin, and Moscow.

While administration officials say Red China is their top challenge, Mr. Biden himself recently phoned President Xi. The Iranian question likely arose in the chat. At the same time, he’s yet to schedule a conversation on Iran with leaders of America’s top Mideast allies — most glaringly with Prime Minister Netanayahu, but also with Gulf states, which, like Israel, are directly threatened by Iran.

Diplomats close to all that frantic Iran deal-related activity say all sides are well aware that the Tehran-backed militias pose a much more acute threat to the region now than they did in 2015, when the JCPOA was struck.

Yet, they quickly add, the Biden administration and the other deal partners prefer to first return to the original framework and only then, perhaps, widen it to include issues like regional aggression, missiles or even Iran’s denial of full access to nuclear inspectors.

If Mr. Biden is serious about addressing such issues at all, he would do better heeding concerns of Iraqi Kurds, Gulf leaders, and Israeli security officials than those of the Europeans, Chinese, or Russsians.