Rigid cordons backfire on mainstream parties

When mainstream parties adopt absolute, inflexible rules of non‑cooperation (a cordon sanitaire) against a growing populist competitor, the result can be local collapse: the competitor wins big, the mainstream party fractures, and ad‑hoc collaborations or illegal tactics proliferate. Sachsen‑Anhalt shows this path: AfD plurality (43.8%) plus CDU fragmentation has already produced fence‑breaking votes and the real possibility of an AfD premier. — This reframes a common tactical question — whether to isolate populists — as a structural risk that can cede large governance space to anti‑system parties if the strategy lacks adaptive flexibility.