Its a military term for a particular form of defensive strategy.

You defend a position against attack until it is no longer possible to do so, then fall back to previously prepared fortifications you have constructed in your rear and set up a new defensive line. And so on. The Wehrmacht was very good at this type of defensive warfare.

This is what our new EPA head is doing. No longer able to deny the fact of global warming, he now essentially concedes the position and falls back on his second line of defense: that global warming exists, presumably it is not a hoax, but it is not the result of greenhouse gases. This gives his pals in the oil industry a few more years of undiluted profit.

I wonder what he has in mind? Cosmic rays? A change in the Solar Constant? Radioactive leakage from nuclear power plants? At one time or another I’ve heard all of these tried on this board.

In other words, anything that doesn’t include the burning of fossil fuels.

http://www.npr.org/sections/thetwo-way/2017/03/09/519425866/epa-chief-scott-pruitt-questions-basic-facts-about-climate-change