Has the US or NATO even threatened to go to war if Russia starts using tacnukes in Ukraine? I haven't seen any reports to suggest so, and I've been following the news on this war closely.

(The US has threatened more sanctions if Russia uses WMDs. That threat was in response to signs Russia was getting ready to use chemical weapons.)

My uneducated guess is that the primary goal of the latest rhetoric about the possible use of chemical weapons is intended to make this more clear. If "we" (not the US yet, but other countries that are nearer) are signalling a readyness to respond kinetically if chemicals are used, surely the message is that nuclear would trigger an even greater response.

China might just drop their support of Russia if that happened.

If a tactical nuke is used, then it is proof that escalation to nuclear weapons does not imply the global nuclear holocaust that has been acting as a deterrent.

It eliminates the logic of not going to war.

Not that "logic" has any connection to "appetite" or that excuses require it.

There's no massive army operating in one place. It's a bunch of units running around in the woods, hills, towns and cities. Their largest forces are probably near the largest Russian forces, so sure, if they're willing to cull their own.

Imagine that this tactical nuclear weapon from 70's fail and expolde over russia territory Or is dropped and do not not work.

Russia would need to make tests and reach readiness to use them, ideally with air superiority.

> The elimination of large chunks of the Ukrainian army in a single detonation could lead to the stated goal of the invasion, which was regime change in Kyiv.

A tactical nuke won't do that, though.

>the stated goal of the invasion, which was regime change in Kyiv.

Where was this stated as the goal of the invasion?

> If Russia did launch a limited tactical strike on Ukraine, let's say super low-yield, honestly not much more than the MOABs we fired off in Iraq, is the USA really going to risk Berlin, or US cities getting vaporized to defend a non-NATO country?

The Baltics and Poland have already been pushing for NATO intervention because they want Russia checked because they don't want to be next; Article 5 is nice, but they’d rather stop Russia before it's on their land.

Nuking Ukraine, even a tiny little nuke, ratchets that up enormously and forces the US and Western European NATO powers to decide how to secure the eastern flank of the alliance.

Ukraine has also not yet attempted to hit Moscow (the city, not the ship) with missiles.

Once a nuclear bomb is used, a lot of gloves will come off, not just the Russian ones, and so far Ukraine appears to have a lot of extremely competent military partners and Russia has a reluctant Belarus.

Something can be a problem without it making sense to worry about it.

If Russia is using nukes, it becomes particularly absurd to continue to follow rules purported to appease them so they don't use nukes.

At best it's a transparently nonsensical excuse that conceals some other motivation.

When important people say they are against doing X, Y, or Z because of the risk of nuclear war, we can at least pretend they are serious as long as no nukes have been used yet.

But is there any other motivation they could have? There's one that seems very obvious to me, especially when I saw the reaction to Lindsey Graham's comments about regime change.

Russia is so weakened I doubt NATO would want them to regain strength if they start dropping nukes.

I presume it would at least make a full embargo more likely?

It doesn't have to be nuclear. Any direct response from NATO would be a losing scenario for them.