Since when have we ever had a policy that allows us to launch or “shoot first”? All I’ve ever heard about is M.A.D. If they fire, we fire. And “they” knew we would shoot back. Now they know there’s a good possibility we’ll never shoot back.
I think past administrations have been careful not to tie our hands for potential crises, especially unforeseen types of problems. “First use” does not only apply to some massive strike option, the question is whether we should rule out forever even one or a small number of, e.g., tactical nukes in some terrible situation. I doubt too many US leaders would give much serious consideration to first use but that does not mean we should constrain ourselves by a “policy” of no first use.