But it was more of a “whatever” intervention, rather than the actual intervention that a red line implies.
But the British House of Commons refused to support the strikes. Worried about alienating Congress, Obama also backed down. On its own by this point, France had no choice but to back down too. François Hollande, then French president, was convinced that this was “a missed opportunity that could have changed the course of the war”.
Western powers opted for the path of diplomacy instead.
Obama isn’t NATO, he’s only a commander-in-chief of a large military that happens to also be a primary member of the NATO treaty.
This red line was still used by the US, Britain, France, etc as a justification to bomb Syria.
https://www.france24.com/en/20180414-syria-chemical-weapons-red-line-obama-macron-assad-russia-usa-france-idlib
But it was more of a “whatever” intervention, rather than the actual intervention that a red line implies.