Cuban migrants rest in a shelter in La Cruz, Costa Rica, near the border with Nicaragua on Nov. 26. (Ezequiel Becerra/AFP/Getty Images)

A year after President Obama and Cuban President Raúl Castro announced with great fanfare their plans to normalize relations, an old source of tension has stubbornly returned, with a rush of Cubans trying to get to the United States.

The number of unauthorized Cubans arriving in the United States nearly doubled in fiscal 2015, rising to 43,159 from 24,278 the previous year, according to U.S. border officials, and the surge appears to be accelerating. The vast majority are coming not in rickety boats or rafts but right through U.S. ports of entry at the border with Mexico. Combined with the more than 20,000 who are issued immigration visas annually under existing accords, it amounts to the largest influx of Cubans into the United States in decades.

“It is three times as large as the rafter crisis of 1994,” said Miami immigration lawyer Wilfredo Allen.

Not since the Mariel boatlift of 1980, he said, when 125,000 landed in South Florida, have so many Cubans headed north.

The migration wave has complicated the Obama administration’s plans to overcome decades of bitter relations with the governments of Fidel and Raúl Castro. It has also revealed the acute sensitivity on the island to any talk — even rumors — of a possible end to the immigration privileges the United States has extended to Cubans for the past 50 years.

The flood of migrants is creating — on a far smaller scale — the kinds of scenes that Europe has experienced as Middle Eastern and South Asian migrants have poured over the borders. As many as 4,000 U.S.-bound Cubans have become stranded in Costa Rica since last month, when Nicaragua stopped letting them pass through. Another 1,000 overwhelmed a tiny Panamanian border town, where officials declared a “sanitary emergency” because there wasn’t enough food, water or shelter. Others are held at immigrant detention centers in Mexico.

Like the asylum seekers streaming into Europe, the Cuban travelers rely on smartphones and social media to share the latest travel information and to keep in touch with friends and relatives who can wire money. A few hire smuggling guides, but most appear to journey in large groups.

So many Cubans are on the move that authorities in Havana and in countries across the region are tightening travel rules. Central American nations are reinforcing their borders. Ecuador has announced new visa requirements for Cubans, sparking rare protests in Havana.

Old and new factors are driving the outflow, from the island’s perpetually pitiful wages to the extraordinary sight of Obama and Castro shaking hands and the American flag flying outside the U.S. Embassy in Havana.

Those images were widely cheered on the island. But they also set off alarms.

Cubans have a saying, “Lo que te den, cógelo,” for the moment when a coveted item such as chicken or laundry detergent arrives at one of the neighborhood bodegas where government rations are distributed. It means, roughly, “Whatever they’re giving, take it.”

It is a rational response to the chronic scarcities of a state-run economy. But the phrase also applies to fleeting moments of opportunity and a particularly Cuban determination to seize them.

Embraced as refugees from totalitarianism, Cubans have for 50 years enjoyed perks offered by the U.S. government to no other immigrant group. The Cuban Adjustment Act of 1966 includes the “wet-foot, dry-foot” rule, which essentially bestows U.S. residency and welfare benefits on any islander who touches American soil.

Cuban American lawmakers are calling for a tightening of the rules, adding to fears of the act’s demise.

Sen. Marco Rubio (R-Fla.) and Rep. Ileana Ros-Lehtinen (R-Fla.) say American generosity is being abused by Cuban migrants who obtain U.S. residency and then begin traveling back to the island to ferry merchandise, run small businesses or get cheap dental work.

To the Obama administration, those Cubans can be agents of change who spread democratic values and a spirit of entrepreneurialism. But older emigres say those circular travel habits make a mockery of the idea that Cubans are so uniquely oppressed that they deserve their own system of political asylum.

The noise of this debate has reached the island, joining the buzz about mending U.S.-Cuba relations. Now, the rush is on.

Cubans have been streaming north by land, sea and air all year. The U.S. Coast Guard picked up 4,462 at sea during the fiscal year that ended Sept. 30 and has retrieved more than 900 since then. Several thousand asylum-seeking Cubans have landed in Miami, flying via the Bahamas or Cayman Islands with European passports issued in recent years to the descendants of Spanish immigrants.

The largest number have come overland from Ecuador, traveling by bus and taxi through Colombia, Central America and Mexico to reach the United States.

In 2008, Ecuadoran President Rafael Correa implemented one of the most liberal immigration policies in the world, essentially opening his country to anyone who wanted to visit. Suddenly Cubans had a place in the region they could fly to without a visa.

Many here began traveling back and forth to Ecuador to buy cheap clothing and other items they could sell on the island’s vast black market. Others figured out how to use the country as a springboard for the 3,000-mile journey to the United States.

It was long, but safer than getting in a boat to cross the Florida Straits.

The protests that followed Ecuador’s reinstatement of visa requirements for Cubans were soothed this past week when the Correa government agreed to issue visas automatically to travelers who purchased their flights prior to the new rules.

In the streets outside the country’s embassy in Havana on Friday, people lined up for hours awaiting appointments, some with bags packed. Dozens of uniformed police officers stood watch, and government technicians set up new security cameras.

No one would admit to plans to use Ecuador as a launchpad to the United States. “It was the only country where we could just buy a ticket and go,” said Maybel Miranda, 36, who lacked a visa but had a ticket for a Dec. 8 flight to Quito. She said she plans to go “for a vacation, and to get some clothes.”

About 40,000 Cubans have established residency in Ecuador in recent years, and many may start heading north if they fear that the window is closing.

U.S. officials insist that the Cuban Adjustment Act will remain unchanged, not least because its repeal would require an act of Congress. Obama has the power to alter elements of it, but State Department officials, in their regularly held migration talks Monday with Cuban diplomats, reiterated that the policy is not up for debate.

Cuban authorities say the Adjustment Act is a huge obstacle to normal relations, and on Tuesday, the Castro government announced that it would reinstate exit visa requirements for most of the island’s doctors, only three years after Raúl Castro eliminated the widely despised travel restrictions.

Cuba has tens of thousands of medical professionals deployed on “missions” around the world, some taking part in humanitarian relief efforts in countries such as Haiti, and others in Brazil, Angola, Qatar and other nations that pay for their services, providing a major source of revenue to the Castro government.

A U.S. program created in 2006 that offers special assistance to Cuban doctors who defect from those missions is a particular sore point for Havana, which singled it out for scorn in a statement issued Tuesday.

“We must remember that the U.S. government has historically used its immigration laws as a weapon against the Revolution, enticing Cubans to leave for political purposes, which has provoked a loss of life, hijackings of boats and airplanes, violent crimes, migratory crises and brain drain,” it read.

So many doctors have left — 1,000 a year, by some estimates — that staffing at Cuban hospitals and clinics has suffered.

Medical professionals in Cuba typically earn less than $100 a month.

The migration crisis in Central America continues as more and more Cubans arrive in Costa Rica, their path still blocked.

On Thursday, Costa Rican authorities said they were negotiating a proposal to airlift the migrants to Belize, where they could presumably try to resume the trip north by sneaking across the border into Mexico.

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