German media outlets Süddeutsche Zeitung, WDR, and NDR also cite the report, noting that Russian President Vladimir Putin appears intent on testing NATO’s Article 5 guarantees. The alliance’s mutual defence clause obliges member states to come to one another’s aid if attacked. The assessment suggests Putin may seek to challenge how seriously that commitment would be honoured.
Considering that Putin got his ass absolutely beat by a small country using second hand and surplus military hardware he'd have to be an absolute moron to pick a fight with NATO. Literally the only card he has to play is nukes and that's kind of an all or nothing sort of move. If nukes are off the table any concerted push by NATO is going to be mopping up in moscow within a few months.
That's also assuming the US doesn't get serious about it, but considering Putin's puppet in the Whitehouse there's a pretty good chance the US would quit NATO and so wouldn't factor in. Even without the US though Russia has demonstrated the rest of NATO is far more than sufficient to handle Russia.