The surge of migrants gathering at the U.S.-Mexico border underscores a point that Democratic Party politicians often try to play down: U.S. border policy has a big effect on how many people try to enter the country illegally.

The current surge is largely a reaction to the looming end of Title 42, a policy enacted during the Covid pandemic that enables the authorities to quickly expel many migrants who enter the country without permission, rather than letting them stay while courts consider their cases. Title 42 expires on Thursday, as part of the end of the official Covid health emergency.

In recent weeks, word has spread in Latin America that entering the U.S. is about to become easier. Smugglers have told potential migrants that the coming period will be a good time to attempt a border crossing, President Andrés Manuel López Obrador of Mexico said last week. U.S. officials believe that the number of illegal crossings per day, which has recently hovered around 7,500, could soon rise above 12,000, according to my colleague Eileen Sullivan.

“It’s a real crisis,” Father Rafael Garcia of Sacred Heart Catholic Church in downtown El Paso told The Times.

When Democrats and progressive activists talk about undocumented immigration, they tend to emphasize forces in other countries — like wars and political oppression — that are beyond the control of the U.S. government. And these outside issues do influence migration flows. The collapse of Venezuela’s economy is a recent example. Experts refer to such forces as “push factors,” because they push people out of their home countries.

But “pull factors” in the U.S. matter as well. The strength of the economy is one. The stringency of border security is another.

When the U.S. makes it difficult for people to enter the country illegally, fewer people make the journey north to try. When the U.S. sends signals that people will be able to cross the border even without permission, and potentially remain here for years, more people attempt to do so.

The pattern is clear. Donald Trump was the most anti-immigration president in decades, promising to build a border wall and demeaning immigrants with racist language. Joe Biden ran for president in 2020 promising a more welcoming approach — and after he won the election, the number of people trying to enter the country without permission spiked:

“There are feedback loops,” Julia Gelatt, a sociologist at the Migration Policy Institute in Washington, told me.

Like so many other political subjects today, immigration has become highly polarized. As a result, the issue’s complexities and trade-offs sometimes gets obscured.

Many Republicans denigrate immigrants. In truth, as research by the economists Ran Abramitzky and Leah Boustan has documented, immigrant families have continued to thrive in recent decades. The children and grandchildren of immigrants have ascended the economic ladder at rates strikingly similar to those of the 1800s and early 1900s.

Democrats have not engaged in anything as hateful as the white nationalist conspiracy theories that are common on Fox News. But Democrats have sometimes brushed aside the hard questions of immigration policy.

A relatively lax approach to border security does have downsides. Early in Biden’s presidency, thousands of people in Latin America left their homes and headed north, often taking enormous risks. Some made it to the U.S. and have given themselves a chance at a better future. Others have languished in crowded and dangerous conditions in northern Mexico — a sign that a porous border creates its own humanitarian problems.

The migration surge of the past few years has also caused problems in the U.S. Social services and shelters in Texas and Arizona cities have been overwhelmed, mayors say. Even some cities far from the border, like Chicago and New York, have struggled to handle the influx. “The president and the White House have failed New York City on this issue,” Mayor Eric Adams of New York, a Democrat, said last month. “Why are you doing this to New York?”

In response, the Biden administration has changed its approach. In early January, Biden announced a tougher policy meant to keep out migrants from Venezuela, Cuba, Haiti and Nicaragua who did not have a good claim of political oppression. The policy also provided new opportunities to come to the U.S. legally.

Immigration advocates and some Democrats criticized the plan as cruel, saying it would deny asylum to deserving refugees. Yet experts say it’s clear that many migrants from these countries are not political refugees. They want to come to the U.S. because it offers better job opportunities.

For the migrants themselves, that calculation is understandable. But no wealthy country permits unrestricted immigration. If the U.S. allowed mass immigration for economic reasons, millions more people would likely try to enter the country.

Biden’s crackdown has started to have its intended effect. The number of illegal crossings fell sharply in recent months (which you can see in the last few bars of the chart above). Now, though, the end of Title 42 has created a challenge. “A lot of people will see this as their chance,” Gelatt said, “or smugglers will use this to lead people across the border.”

To reduce the surge, Biden has dispatched 1,500 troops to the border. The troops are there to manage the chaos — and to send a message: The U.S. does not have an open border, and most people who try to enter the country illegally will not succeed.

N.B.A. playoffs: The Philadelphia 76ers tied their series last night, defeating the Boston Celtics, 116-115. And the Phoenix Suns are now tied with the Denver Nuggets in their series.

Bumped: But all eyes were on the Phoenix owner Mat Ishbia, who got into a courtside tussle with Nikola Jokic.

Red Bull battle: Max Verstappen won the Miami Grand Prix.

Leafs in trouble: After winning a first playoff series in nearly two decades, the Toronto Maple Leafs find themselves in another dire situation, down 3-0 to the Florida Panthers.

Boxed wines have a bad reputation with producers and customers, but they make ecological sense, the Times critic Eric Asimov writes. “The carbon footprint is about a tenth of the emissions for the production of four single-use bottles, not even taking into consideration weight and transport,” said Melissa Monti Saunders, the chief executive of a wine ‌importer and ‌distributor. “‌No way around it, b‌oxes are significantly better for the planet.”

The pangrams from yesterday’s Spelling Bee were loveably and volleyball. Here are today’s puzzle and the Bee Buddy, which helps you find remaining words.