What is the meaning of "to be next into the breach" in the following examples?
There's a blue flame from, I think, an oxygen tank. Carter finds Lisa on the floor and asks her if her neck is okay; she nods. Luka is next into the breach, and asks Carter whether Lisa's airway is clear[.]
The idea that English has more than one declarative “mood” has been dismissed as superstitious by empirically-minded grammarians of English for centuries [. . .]. Let me be next into the breach.
But let's be of good cheer: looks like Newt the execrable is next into the breach as the transitory not-Mitt.
I can sort of grasp the overall meaning—it seems to me that a simple next would do the job in all the examples above—but I can't figure out its connotation: what does "into the breach" add to the sense? Does this idiom change its meaning according to the context?