A plurality of Justices O'Connor, Kennedy, and Souter reaffirmed what they called Roe's 'essential holding' but discarded the trimester framework in favor of an 'undue burden' test — a state may not place a substantial obstacle in the path of a woman seeking a pre-viability abortion. Casey governed abortion doctrine for thirty years and, notably, contained an extended defense of stare decisis whose reasoning Dobbs later rejected.