3/4 of the states' legislatures.
That means that only 13 states have to say "no".
Sorry, I thought it was 2/3 but an insurmountable task in any case. Elsewhere I replied to a post about the possibilities of a Dem majority on SCOTUS and how they can ‘amend’ the Constitution by interpretation. I.e., finding an inarticulated “right” within a penumbra.