Setbacks in the quest for universal health coverage in Mexico: polarised politics, policy upheaval, and pandemic disruption.

2023 marks the 20-year anniversary of the creation of Mexico's System of Social Protection for Health and the Seguro Popular, a model for the global quest to achieve universal health coverage through health system reform. We analyse the success and challenges after 2012, the consequences of reform ageing, and the unique coincidence of systemic reorganisation during the COVID-19 pandemic to identify strategies for health system disaster preparedness. We document that population health and financial protection improved as the Seguro Popular aged, despite erosion of the budget and absent needed reforms. The Seguro Popular closed in January, 2020, and Mexico embarked on a complex, extensive health system reorganisation. We posit that dismantling the Seguro Popular while trying to establish a new programme in 2020-21 made the Mexican health system more vulnerable in the worst pandemic period and shows the precariousness of evidence-based policy making to political polarisation and populism. Reforms should be designed to be flexible yet insulated from political volatility and constructed and managed to be structurally permeable and adaptable to new evidence to face changing health needs. Simultaneously, health systems should be grounded to withstand systemic shocks of politics and natural disasters.