Before 1 January 2020, will a NATO member formally invoke Article 4 or Article 5 of the Washington Treaty in response to actions taken by Russia?
Article 4 has been invoked a few times in the history of NATO (NATO, Radio Free Europe). Article 5 has been invoked just once (NATO, NY Times). If Article 4 or Article 5 is invoked for an event in which the perpetrator is initially unknown and NATO subsequently attributes that event to Russia, the question will close retroactively with the end date of the invocation.
The question closed as "No" with an end date of 1 January 2020.