A Lunar base & ISRU effort was not just a theory that existed, but the predominant conventional wisdom in NASA's planning, ten years ago. And it was a bit sill

A Lunar base & ISRU effort was not just a theory that existed, but the predominant conventional wisdom in NASA's planning, ten years ago. And it was a bit silly even before they did the typical NASA thing of underfunding and cancelling essential bits in the bureaucratic infighting. ISRU on Luna is likely to be an effort with comparable scale to a Mars mission, with questionable amounts of translatable techniques. Most anything we can do on Luna other than ISRU, we could do in LEO. Luna is seen as a sort of cheaper prize than Mars by Lunar proponents who don't advocate 'stepping stones', but the cost of operating on Luna via Constellations is higher than the NASA HSF budget today, and would likely prevent serious attempts at Mars planning in the same way the ISS/Shuttle is doing today.