> So what, would you say, triggered the US to cross their own red line...

I'd first reject the use of the term "red line" entirely for the ATACMS situation.

"No, not ever" is a red line. The Russians love issuing these for other people, but it's embarassing when they're crossed without significant consequence.

"No, not now" is not a red line. The US tends to shy away from issuing them - one of Obama's biggest mistakes was proclaiming one in Syria and then looking a bit feckless when they violated it. (https://www.pbs.org/wgbh/frontline/article/the-president-bli...)

Letting Ukraine hit Russian territory with ATACMS is like the fourth or fifth expansion of how they're permitted to use that weapons system so far, as was giving them ATACMS in the first place after HIMARS (which saw a similar set of gradually reduced limitations; https://www.defensenews.com/land/2022/07/08/us-to-send-more-...).

> And, backtracking, how aware have you been about the situation in Ukraine, or baltic sea infrastructure, in the past few months (even year), compared to the last week? Just a marginal increment, no doubt.

I've closely followed the situation in Ukraine since Euromaidan.

"I'd first reject the use of the term "red line" entirely"

No doubt, but the fact is the US told Ukraine they couldn't use ATACMS to target Russia, and now, they can.

And it's really more than an incremental change in US involvement in the war. The fact that Ukrainians are supposedly operating these weapons is almost incidental.