Surprised I had to scroll down to see this. Collective defense means expanded nuclear umbrella from the nuke powers in NATO. TFCMA/WP/Russian doctrine has always allowed a free hand for local commanders to use tactical weapons - a very tempting option to deal with Sweden[1] in the event of a Baltic/Kaliningrad land grab. Admission to NATO is a barrier to that, since the West doesn't exactly believe in small bites when it comes to nuclear weapons. Tactical nuclear weapon usage against member states would very likely have a strategic response.

[1] And Finland, which is also coming over.

You mean the USA will launch nuclear missiles on Moscow in case Russia launches a missile on Stockholm?

NATO or not, I have my doubts here. Does anyone believe any sane US president would risk a destruction of the USA to revenge / protect Sweden?

Failing to respond would invite salami-slicing tactics.

Likely not on Moscow, but on some city similar in size to Stockholm.

It's of course unclear what would happen, but I don't think Russian strategy can rely on US not responding.

What city? Striking any city on Russian soil will provoke a full on retaliation of the USA.

Equivalent retaliation would be targeting a city of some of the Russian allies, but it's not possible since Russia doesn't have allies ;)

So long as the Russian decision makers believe they will be hit with nukes if they use nukes themselves, it doesn't matter precisely which target — the point of MAD is a deterrent that prevents the nukes getting used in the first place.

If the decision makers think "we can use as many nukes as we want because we have a huge stockpile and can level anyone who even tries to respond in kind", we're already on borrowed time.

Strategic reaction doesn’t necessarily mean a capital atomic strike. It can be a range of responses that have been off the table during the Ukraine war so far. Switching the entire economic output to a wartime posture for example, is just as strategic.

I think it is in Russian elites’ and Putin’s self interest to continue the status quo and grind down the West in Ukraine, plunder it, and leave the long-term consequences to Russia in someone else’s hands. I’m doubtful they’ll actually use atomics unless the walls are violently closing in. Even China backed way off when Putin loosely waved around nuclear rhetoric in the opening months of the war, and asked in nervous diplomatic speak, “chill, broseph”.

To be precise Article 5 requires the countries to consider an attack on Sweden to be an attack on them, and they shall respond as they see fit.

In an actual attack, they may see fit to do nothing - it will come down to the circumstances.

In other words, if Russia attacks Sweden and the US decides to ignore it, there's not much NATO can do but kick the US out.