Miguel notes some history of the concept, from 117 years ago, in two federal cases from 1895 and 1921. That’s right folks, there’s no duty to retreat under federal law, and that’s been the case since 1895 at least, and this duty was not unknown prior to this as well, as most western states never required such a duty, including California, which was admitted into the Union in 1850.
As a side note, I normally would not advocate debating CSGV, as opposed to pointing and laughing, since it’s about as pointless as beating your head against a wall, and about as entertaining as watching the grass grow. But you’ll note the other person involved in that conversation is a CNN legal analyst and anchor. If there’s even a chance that you can raise some doubt about CSGV’s, ahem, honesty, that’s worth beating your head against a wall for a little bit, don’t you think? She has a pretty interesting legal background. Clerked for the Chief Justice of Maryland’s Supreme Court, and worked for a bit as an AUSA in D.C.