A fatal strike in Poland involving a 'Russian-made missile' could pose biggest test yet to Biden's vow to defend 'every inch' of NATO territory

• An apparent missile strike in Poland killed two. Zelenskyy blamed Russia, but much remains unknown.

• Poland is a NATO member, and there's rampant speculation about the implications of this incident.

• The reported strike could pose a major test to Biden's vow to defend "every inch" of NATO territory.

President Joe Biden has repeatedly pledged to defend "every inch" of NATO territory since Russia launched an unprovoked invasion of Ukraine in late February, drawing a clear red line for Moscow. Biden's vow could be facing its biggest test yet following fatal strike in Poland, a NATO ally, that the Polish foreign ministry said involved a "Russian-made missile."

The Pentagon echoed Biden's promise on Tuesday. "When it comes to our security commitments and Article 5 we've been crystal clear that we will defend every inch of NATO territory," Pentagon spokesperson Brig. Gen. Patrick Ryder told reporters during a briefing.

The explosion in Poland, which reportedly killed two in the town of Przewodów, came as Russia carried out missile strikes across Ukraine on Tuesday. Details are still hazy and it's unclear if what happened was the result of a deliberate attack. The White House said it could not confirm the reports and will work to "determine what happened and what the appropriate next steps would be." Meanwhile, Russia's defense ministry denied reports that Russian missiles hit Polish territory, dismissing the allegations as a "provocation." Biden later told repoters, "It is unlikely in the lines of the trajectory that it was fired from Russia, but we'll see."

"I'm going to make sure we figure out exactly what happened," the president said. "Then we're going to figure out our next step."

But if it's confirmed that Russian missiles struck Poland, whether accidental or not, it would mark the first time the war in Ukraine spilled over into a NATO country and led to casualties. Along these lines, this could prove to be a major turning point in the conflict.

"We're drilling down to find out what were the circumstances of it. It's obviously very important to understand — was it a mistake, was it an overflight, was it intentional? I hope that it was not intentional," Democratic Sen. Bob Menendez, chair of the Senate Foreign Relations Committee, told Politico.

"Obviously if it was intentional, that has all kinds of consequences to it," Menendez said, adding, "It's definitely an enlargement of the conflict, and of course, it brings into question Article 5."

A direct confrontation between NATO and Russia could be catastrophic. Russia possesses the world's largest nuclear arsenal and multiple NATO members are nuclear powers. Along these lines, Western officials are being cautious as they react to this.

NATO chief Jens Stoltenberg said he spoke with Poland's president about the explosion and offered his condolences, adding that the alliance "is monitoring the situation and Allies are closely consulting."

"Important that all facts are established," Stoltenberg said.

NATO operates under the principle of collective defense, which is enshrined in Article 5 of its founding treaty. It considers an attack on one member an attack on all. But Article 5 has only been invoked once in NATO's history — following the 9/11 terror attacks against the US.

Article 5 is not automatically triggered in the event that a member is attacked. In theory, if a member country was attacked it could request Article 5 to be invoked, or members could come together and discuss whether such an event warranted invoking it. Members could decide that an accidental strike does not constitute an armed attack worthy of the alliance's collective-defense mechanism.

And even if Article 5 is invoked, it does not commit or oblige other members to respond with military force. Article 5 states that NATO members will assist the attacked party or parties by "taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area." In short, the language of Article 5 offers members leeway in terms of how they decide to support an ally.

Ben Hodges, the former commanding general of the US Army in Europe, in a tweet on Tuesday said, "Dear friends, there is no such thing as 'triggering' Article 5. It's not automatic. There is no laser beam that opens a door like at a hotel or store if you walk through it."

Hodges added that Article 5 is a political decision, and Article 4 consultations seem more appropriate until more facts are available. Article 4 of NATO's treaty allows for any member to request consultations when "the territorial integrity, political independence, or security of any of the parties is threatened."

The Polish government, which reportedly held an emergency meeting in response to Tuesday's events, is considering invoking Article 4, according to reports. Polish President Andrzej Duda in comments on Tuesday said Poland does not have solid evidence showing who fired the missile. "It was most likely a Russian-made missile, but this is all still under investigation at the moment," Duda told reporters.

Still, if it's determined that Russia attacked a NATO country deliberately, it could put Biden under immense pressure to respond in a forceful way.

The president has used strong language in reference to Article 5 and the US's obligations. "We have a sacred obligation under Article 5 to defend each and every inch of NATO territory with the full force of our collective power," Biden said in March. The US is the most powerful member of NATO and has been the top provider of security assistance to Ukraine. In this capacity, Washington would be expected to take a leading role in any response to an attack on a NATO member.

The explosion in Poland led Biden to call an emergency meeting of G7 and NATO leaders while in Indonesia for the G20 summit. Biden also spoke to Duda by phone, and offered the full support and assistance of the US while reaffirming the US's "ironclad commitment to NATO," the White House said.

Though much remains unknown about what happened in Poland, the Ukrainian government is already pushing for a firm response. "The longer Russia feels impunity, the more threats there will be to anyone within reach of Russian missiles. To fire missiles at NATO territory! This is a Russian missile attack on collective security! This is a very significant escalation. We must act," Ukrainian President Volodymyr Zelenskyy said in his nightly address, per Reuters. Kyiv has desired and called for increased NATO involvement in the war from the start of the conflict.

What happens next is up in the air, making this one of the most uncertain moments in the war to date.

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