After more than 50,000 migrants surged from Morocco into the Spanish territory of Ceuta, in North Africa, leaders of all political backgrounds either blamed the crisis on the pro-immigration policies of Pedro Sánchez, Spain’s left-wing prime minister, or raised concerns about them.

Spain’s leading far-right politician traveled to Ceuta to blame Mr. Sánchez directly. The centrist leaders of Denmark, Germany and Poland signed a letter expressing “serious concern” and a need to address “all policies that can serve as pull factors.”

Lost in the criticism was how quickly most of those migrants returned across the border. By Friday morning, less than 24 hours after the breach, a long line of mostly young Moroccan men marched barefoot, hungry, thirsty and exhausted back to Morocco.

Rather than welcome the migrants, Mr. Sánchez had called in the military. Most of the arrivals this past week were given no access to food, water or accommodation — unlike in 2015, when Europe’s mainstream leaders gave shelter to Syrian refugees arriving en masse to the continent. Soldiers in Ceuta used loudspeakers to blast messages in Arabic telling the migrants to leave. Some police officers occasionally slapped barefoot stragglers on the backs of their legs with truncheons to keep them moving back to the border.

“In less than 48 hours, my government has succeeded in fully restoring control over the border,” Mr. Sánchez wrote on Saturday in a response to criticism from partners in the European Union. Spain had succeeded in returning “virtually all of the migrants who crossed irregularly,” he added.

Mr. Sánchez’s reaction to the Ceuta crisis, which Spain said had left more than 70 migrants dead, has highlighted that he has a more complex approach to migration than either Mr. Sánchez’s left-wing supporters or right-wing critics like to acknowledge.

Mr. Sánchez became a global liberal darling in part by pursuing pro-immigration policies, especially by welcoming Latin Americans and allowing unauthorized immigrants to apply to legalize their status. That set him apart from most other leaders in Europe, including center-left leaders who have soured on immigration since 2015, and from President Trump.

But that warm approach to some immigrants, specifically those already in the country or who landed legally at Madrid airport, has deflected attention from Mr. Sánchez’ much tougher approach to immigrants attempting to illegally cross Spain’s borders with Morocco.

Mr. Sánchez, in power for nearly a decade, has never repealed the previous conservative government’s 2015 law allowing instant expulsions of immigrants crossing Ceuta’s border. That is one of the most punitive laws in Europe, where migrants are, officially at least, usually allowed to apply for asylum. His government has furnished surveillance equipment and stationed intelligence officers in Africa to keep migrants from coming to Spain. It has also pursued hard-eyed, behind-the-scenes deals with the authoritarian government in Morocco.

Those deals, Mr. Sánchez wrote in his letter on Saturday, helped reduce “irregular arrivals through our territory dramatically” and, more than his right-wing neighbors, he said, made Spain one of the “most secure” external borders in the bloc. According to European Union data, migration flows toward Spanish territory since 2021 had been substantially lower than to Greece and Italy, whose governments are perceived to have taken a tougher line against illegal immigration.

His rhetorical pivot was vintage Mr. Sánchez, whose political survival skills have long vexed his critics. This month, he used the worst wildfires in the country’s history to attack climate change deniers in the opposition and repel criticism that his government had not worked hard enough to proof Spain’s arid landscape from fast-spreading blazes. He has tried to dilute the impact of corruption scandals involving his inner circle by casting some of them as politically motivated.

Now, he is seizing on a blaring violation of Spain’s border security to argue how effective his government has been at pushing back migrants and cutting down on illegal immigration more generally.

Even for a politician with Mr. Sánchez’s talent for spin, it was a stretch to cast the violation of Spanish sovereignty by tens of thousands of migrants — all caught on camera and broadcast as essentially a right-wing highlight reel — as a victory. But Mr. Sánchez was giving it a shot.

Throughout the weekend, his government took credit for what it called the “voluntary returns” of tens of thousands of Moroccans. Many of those migrants described their return as anything but voluntary. Many said they had expected a warmer welcome and job opportunities in Spain, and instead had found hunger, thirst, exhaustion and uncompromising police officers, who chased them from the center of Ceuta’s streets into the long parade back toward the border.

A spokesman for Fernando Grande-Marlaska, the interior minister, declined to comment on whether there was an explicit government strategy to deprive the migrants of essentials. The Interior Ministry said only that officials were “providing care within the scope of our responsibilities.”

That scope seemed less than broad. On Sunday, soldiers tried to take some groups of migrants back to the border on their trucks. Hundreds of others, who had decided to stay in Ceuta, were denied access to the territory’s overflowing migrant center and stayed on a portion of the beach.

In general, Mr. Sánchez’s government has for years worked with the Moroccan government to prevent migrants from getting close to Ceuta.

In an interview late last year, Mr. Grande-Marlaska hailed Spain’s partnership with Morocco and dismissed concerns from rights activists about working so closely with the country’s authoritarian government.

Morocco “is a very loyal partner,” Mr. Grande-Marlaska said at the time, adding, “It is doing important work in preventing and combating irregular migration.”

He also expressed concern that a government plan to allow illegal migrants already in Spain to apply for formal paperwork could act as what he called “a pull factor” for future migrants.

This spring, the government enacted just that plan.

In recent days, the government has suggested that the initiative, and its pro-immigration policies in general, had little to do with the surge into Ceuta. They blamed instead the misinterpretation of a recent Supreme Court decision which suggested that migrants who reached Ceuta by sea could not be summarily expelled. Smugglers used that misinterpretation, they said, to spread misinformation about an open border.

Mr. Sánchez’s critics in Spain, Europe and elsewhere weren’t exactly sympathetic. Far-right leaders lined up to portray Ceuta as a vivid vision of the dangers of illegal migration, a real-life manifestation of the nightmare they had been warning about for more than a decade. Centrist leaders, anxious to avoid being outflanked on a potent issue, called for greater immigration controls on Spain.

Despite Mr. Sánchez’s arguments to the contrary, the perception across Europe was that he had lost control.

“Pedro Sánchez appears on my social media,” said Ammour Moussa, 19, from Sudan, who was one of the hundreds of migrants who were still on the beach in Ceuta on Sunday evening. “We have heard from different sources that he is willing to accept more immigrants — but we don’t know how many or when.”

Carlos Barragán contributed reporting from Ceuta, Spain.