Be a little bit careful with this: Don't confuse Article 4 with Article 5.

Article 4 creates an urgent conversation between NATO member diplomats on collective security, but has also happened several times in the past. Don't confuse it with Article 5, which is invoking the mutual defense treaty obligation in response to an armed attack.

But still Article 4 is a substantial step, and an indication of how serious #Poland is taking it.