Ukraine is the defender in this conflict. Every reasonable action it takes to encourage a Russian withdrawal is, by definition, defensive.
The US is publicly signalling that this might not be going far enough to pressure the Russian homeland.
The intent is to put pressure on the regime, not the "homeland".
This attitude floors me. I can't figure out if people legitimately believe that we can just ignore the nuclear war risk [...] or if the plan is to purposefully explore for a limit where Russia snaps.
There shouldn't be any mystery to this. The intent is to help the current regime in Moscow come to the only rational decision available to it, which to stop the war it should have never started in the first place. There is no intent to make it (and certainly not Russia as a country) "snap". That's just your projection.
On the contrary, the intent it is to help the regime come to its senses. Like the US was finally forced to do in Vietnam, Iraq and Afghanistan.
And in parallel, to save Ukrainian lives, especially civilian lives -- which are being lost daily due to attacks launched from within Russian territory