That wasn't a red line, any more than NK's weekly promises to unleash nuclear war over the slightest provocation. NK can't cross a red line that doesn't exist.
If the world can't take the US's word seriously on matters of foreign policy that's a huge fucking problem (albeit, admittedly, less of a problem than nuclear war).
No reasonable person understood it as a genuine red line, so no credibility will be lost.
Like, asking NK not to threaten? That's like asking someone to stop breathing. It's about as plausible as the German ultimatum to Belgium in 1914. Threatening others is the foundation of the existence of the North Korean state.
There was no way they would comply with that, meaning either it was not a red line but just bluster, or it was an ultimatum designed to offer a pretext for a war. But I think everyone knew it wasn't the latter, from the moment it was said.
"Everyone knew it wasn't credible, so no credibility is lost"? ---