A Puzzling Move by a Political Survivor Grips Spain

A wave of political turmoil crashed over Spain on Thursday as Prime Minister Pedro Sánchez publicly weighed resigning his post after a judge agreed to investigate his wife over allegations that he and other officials decried as a politically driven smear campaign.

The judge’s decision to take up the case — which was brought by a self-described anti-graft group on the basis of online news reports about alleged influence peddling — prompted Mr. Sánchez’ssupporters to coalesce behind him and public prosecutors to move quickly on Thursday to try to get the case dismissed.

Mr. Sánchez, whose political survival skills have for years astonished his supporters and detractors alike, wrote in a public letter Wednesday that the accusations against his wife, Begoña Gómez, were false and amounted to harassment. One of the most prominent leftist leaders in Europe, Mr. Sánchez has canceled his public schedule while he reflects on his next move. He plans to address the nation on Monday.

As Mr. Sánchez holed up with his family and resisted the entreaties of his allies to hit the campaign trail ahead of key elections in the Catalonia region and for the European Parliament, supporters talked about mobilizing rallies to convince him to stay.

And a wide array of Spaniards, from the political elite to citizens on the streets, expressed bewilderment at the uncharacteristic retreat by a prime minister who only recently had reclaimed his post in elections last summer, and by the country’s odd state of affairs.

“It’s a mess,” said Pablo Simón, a political scientist at Carlos III University in Madrid, who said he was struck by the deeply personal tone of Mr. Sánchez’s letter. He added that the investigation into Mr. Sánchez’s wife of 18 years had apparently triggered an emotional reaction, because, politically speaking, “there were no clear incentives for this gambit, it’s very risky.”