I interpreted Biden's response, based on his decades of saying non-literal, silly, exaggerated stories, and many times eyebrow-raising comments, as such:
-We will shoot down chemical weapons in the air.
-We will destroy facilities/equipment that launch chemical weapons.
And he would limit it to just targeting the chemical stuff, not blowing it up into a full scale war. But to do that, Congress would be outraged without a vote first. Enough of Congress has thrown a fit over not getting says in smaller conflicts, how much bigge of a deal that would be with Russia. Technically, Presidents have some warring flexibility for up to 60 days of fighting, permitting they notify Congress within 48 hours, and have to begin pulling out troops on day 61 I believe. And enough of the population wants us to do a lot more than we are now that he could be embolden to strike those locations if Putin crosses that line, that he may ignore the outrage in Congress.
But if he just strikes targets and doesn't send troops in I guess it won't even trigger that clock.