Pedro Sánchez, Spain’s interim and perhaps soon-to-be (again) prime minister, is no stranger to taking risks. But his latest gamble has triggered a massive backlash from broad swaths of Spanish society, including in his own party, that threatens to tear the country apart.

To break a monthslong deadlock after an inconclusive general election in July, Sánchez has struck a controversial political agreement with Catalan separatist parties to grant them amnesty for all charges related to the failed 2017 independence referendum in Catalonia, the northeastern part of Spain. Sánchez’s Socialist Party (PSOE) came a close second in the elections to the mainstream conservative Popular Party, though neither won close to a majority.

Thanks to his horse-trading, Sanchez now has the necessary votes to renew a coalition government with support of the far left and formerly standoffish Catalan regional parties. He could regain the premiership this week if legal challenges don’t stop the effort. But it comes with a huge price tag…