Could the next big story out of Afghanistan be the emergence of a full-scale civil war? We ask because new reports suggest that the long-running struggle between the Taliban and ISIS-Khorasan, the Islamic State’s branch in Afghanistan, is heating up. And a full-scale civil war would raise all sorts of issues for America itself and our friends and allies, from Europe and the Middle East to the sub-continent and Asia.

Just this past weekend, in a series of seven or eight bombings near Jalalabad, 80 miles east of Kabul, ISIS-K blew up several Taliban convoys. “More than 35 Taliban militia members were killed or wounded,” Reuters reported, quoting a statement it says was made on ISIS-K’s Telegram channel. That is only the latest skirmish between the two groups in a fight that has gone on for years.

That report comes on the heels of the Taliban’s execution of the former leader of ISIS-K, Abu Omar Khorasani, and eight other members of his group. This might not be quite the flashpoint that the assassination in 1914 of Archduke Ferdinand turned out to be, but we find ourselves thinking: What will America do if the struggle erupts to the next level? Particularly because our departure has made this civil war more likely.

Under President Trump’s deal with the Taliban, after all, we Yanks focused our fire against ISIS-K, leaving the Taliban alone. We’ll leave aside the question of whether we should have been treating with the Taliban at all (the Sun was against it). And set aside whether Mr. Trump would have flubbed our departure the way Mr. Biden did. The fact is that in the wake of the departure of our forces, ISIS fighters are under much less pressure.

What happens if ISIS-K seizes territory and establishes a caliphate like it did in Syria and Iraq? This is not unlikely, and it wouldn’t be the first time. As recently as 2016, ISIS controlled several Afghan districts. Would Mr. Biden help the Taliban fight the Islamic State in these circumstances? In a certain light, after all, Mr. Trump’s earlier decision to focus our fight on ISIS-K rather than the Taliban could constitute support.

If Hitler invaded hell, Churchill might have been prepared to make in the Commons a favorable reference to the devil. Is the Taliban that is the enemy of our enemy (ISIS) our friend? No, we say, but Chairman Milley of the Joint Chiefs seems open to the idea. Asked at a press conference about possible “coordination” with the Taliban, the general said “it’s possible.” That was after declaring: “In war, you do what you must.”

How much support, if any, are we considering for the Taliban and of what type? Intelligence? Arms? Advisors? Air strikes? Boots on the ground? If we do throw in with the Taliban, would that make us their partners? Or facilitators? Would air strikes make us the Taliban’s de-facto Air Force? Would we give the Taliban whatever it might take to defeat ISIS? Then again, too, if we don’t, what would be the consequence of that?

What would happen were we to let ISIS-K control territory and establish a caliphate in Afghanistan? Would that mean we’ve given up our world-wide fight against global terrorism? According to Secretary Austin just three weeks ago, defending our nation means “relentless counterterrorism” against “any threat to the American people, any place. It means working with our partners to shore up stability in the region around Afghanistan.”

Hmmmm.

One thing is clear. President Biden’s precipitous withdrawal from Afghanistan has put us in a precarious pickle. Mr. Biden has a lot to figure out. He doesn’t seem to have much in the way of answers, and no one seems to be asking the questions. We could have retained a permanent military base with roughly 3,000 troops, and been in a far better position to avoid the predicament into which Mr. Biden has found himself.

The ramifications are only just beginning and will not stop with the refugees we’ve welcomed to America and the people we’ve abandoned. Mr. Biden was shockingly blithe about all this when he addressed the United Nations yesterday. As the diplomats applauded Mr. Biden, we found ourselves thinking of Premier Daladier, who, cheered by the crowds on his return from Munich, muttered to an aide, “Ah, les cons . .”