Klaus Welle is the Chairman of the Martens Centre Academic Council.

“The Greenland incident changed thinking about NATO Article 5 and US reliability. So, we have our own solidarity clause which hasn’t been operationalised,” said Klaus Welle, a long-time Brussels insider who served as secretary‑general of the European Parliament for 14 years.

[…]

Despite the apparently wide-ranging nature of the EU’s mutual defence agreement, Welle – who currently leads the centre‑right Martens Centre advisory council and advises the Commission on defence matters – said it’s unclear what the response would look like if a country actually triggered Article 42.7.

For example, if 100,000 Russian troops suddenly appeared on the eastern border of one of the Baltic countries and the US, for whatever reason, signalled it would not engage in conventional defence under Article 5, there are questions over how the European Union would act, according to Welle.

“Europeans have to say what would happen exactly if Article 42 were activated,” Welle said.