I use quantitative textual analysis of the Israeli Knesset’s legislative debates to analyse legislative parties’ strategies. The analysis demonstrates three results. First, given an opportunity provided by an exogenous shock to the Israeli political system, dovish opposition parties used their floor speeches strategically to emphasize a frame of Israeli security on which the hawkish majority held a losing position. Second, due to its weak position, the hawkish coalition eventually ‘deserted’ the frame. Third, this dynamic resulted in a major change in the legislative discourse on security, and in the consolidation of a frame of security that highly favoured the opposition. I argue that this strategy constitutes rhetorical heresthetic, since it emphasizes the internal contradictions of the majority and contributes to its split. In general, these results demonstrate that legislative rhetoric is an important venue of oppositional behaviour, especially given the limited agenda control the majority has over legislative speeches. Finally, the model is generalizable to measuring dynamic partisanship in various political institutions.