For the first time since Russia’s full-scale invasion of Ukraine, a NATO member has formally invoked Article 4 of the alliance’s founding treaty after a major airspace breach. Estonian Foreign Minister Margus Tsahkna tells Talk to Al Jazeera why repeated Russian provocations are more than isolated incidents – they’re a test of NATO’s credibility. As United States President Donald Trump questions the value of collective defence, Tsahkna warns that Europe’s security consensus is fraying and hesitation could invite danger.