In other words, this subject is not going away. And increasingly, the White House is dealing with it in a very specific way: by invoking World War III.

Biden briefly mentioned the possibility at the start of the invasion in late February, telling an interviewer the choice was between sanctions and “World War III.” And over the past week, Biden and White House press secretary Jen Psaki have repeatedly sought to point out that no-fly zones and such measures would likely be or amount to the launch of the Third World War.

Pressed by the decision not to supply military aircraft to Ukraine last week, Psaki replied: “Well, I would say our assessment is based on how to prevent a world war here.”

The following day, Biden mentioned World War III four times in two separate appearances.

“The idea that we’re going to send offensive equipment and have planes and tanks and trains with American pilots and American crews, just understand… it’s called World War III, okay? Let’s get it straight here, guys. He added that “we will not fight World War III in Ukraine”.

On Monday, PSAKI said that “starting World War III is certainly not in our national security interests.” And on Wednesday, she linked it to a no-fly zone, saying: “It would potentially force us to shoot down Russian planes – NATO shooting down Russian planes. And we are not interested in entering World War III.

There is no doubt that something like a no-fly zone would lead to a direct military confrontation between the United States and Russia; even proponents of the idea have acknowledged this. Whether this conflict would mean another world war depends on how you define it.

The “world war” actually only became popular well after the end of the mostly European conflict of 1914-1918, known then as the Great War. When a similar conflict began, Time magazine in 1939 suggested that it could soon become “World War II“.

Generally speaking, a world war is defined as a war that involves many countries around the world and/or several leading countries. A war involving the United States and Russia would surely involve two of those nations, and it’s hard to see the United States getting involved in such a thing without other NATO nations.

In recent decades, the concept has rarely been brought up in other conflicts. But not like today. (Biden, for example, spoke dismissively in 1994 of concerns in Europe that Bill Clinton’s “stand and strike” proposal for Bosnia would lead to World War III. “Sarajevo 1994 is not Sarajevo 1914,” Biden said.)

It’s in many ways an acknowledgment of a very possible reality – even if it’s shocking to hear. This is Europe’s first major ground war in decades, after all, and there are indications that Russia’s intentions could extend far beyond Ukraine alone, creating the possibility of conflict with the countries of NATO which would necessarily encourage them all to act in common defence.

Maybe it’s because it reassured people that we’re not really headed in that direction. But either way, it serves as a useful tool to quell any militarism that may arise in the days and weeks ahead. No-fly zone? Just know what it means. Zelensky wants more? Just know what it means.

Of course, to make this point, you have to continually insist that this is a real enough possibility to talk about in the first place. Asked about Biden’s comments about the risk of World War III by NBC News on Wednesday, Zelensky didn’t disagree – but instead suggested it may be inevitable or has already begun.

“No one knows whether it may have already started,” Zelensky said, “and what is the possibility of this war if Ukraine falls?”

And it also means that such actions that you might later feel compelled to take – no matter how hard you try to rule them out now – will be hard to play as anything less than indicative of that kind of historical escalation.