Article 5 doesn’t automatically get triggered once a NATO member is attacked; the country attacked needs to request that the alliance invoke it. In this case, that would mean Poland, should Polish officials conclude that Russian missiles were sent deliberately.

What does triggering either require of the US?
Under Article 4, all NATO members, including the U.S., are required to join discussions at the North Atlantic Council, the alliance’s main decision-making body. That could be followed by a joint declaration or plan of action.

Invoking Article 5, however, has more serious consequences. It means that the United States would be called upon to help defend any European ally, or Canada, if attacked.

But there is an important caveat. Article 5 was written in such a way that it allows each ally to decide for itself the best course of action to take – there is no prescribed response once the article is invoked.

In the case of the U.S., the executive branch – that is, the president – would need to consider the views and responsibilities of Congress. If the president were to decide on direct military action, then Congress would likely be involved in some capacity – and, of course, only Congress has the power to declare war.

But Article 5 doesn’t necessarily require a military response. In fact, there is enough flexibility in the language of the treaty for a more nuanced response.

This is vital. Each member of NATO remains a sovereign state and can’t be compelled into military action. Decision-making over the use of force remains at the national level; such choices are not simply handed over to a supranational organization.

https://theconversation.com/poland-responds-to-russian-drones-incursion-by-invoking-article-4-of-the-nato-treaty-what-happens-next-265051