The debate over border security in Congress is ultimately about whether the United States should accept much more immigration than federal law allows.

To many Democratic politicians and immigration activists, the answer is yes. They believe that the U.S. has a humanitarian responsibility to admit millions of migrants who live in countries that are poorer or beset by turmoil. These immigration proponents believe that the proposals in Congress to toughen border security are cruel and xenophobic, needlessly turning away people who are eager to contribute to American society.

To many Republican politicians — and most voters, polls suggest — the porous southern border is an urgent problem. Since President Biden took office, the number of people apprehended at the border (a proxy for flows of illegal immigration) has risen more than fourfold compared with the average level in the 2010s. The data suggest that thousands of people are entering the country illegally each day. This surge has created chaos in parts of southern Texas and Arizona and has strained resources as far away as Chicago, Denver and New York.

The Senate has remained in session this week, rather than starting its holiday recess, so that its members can continue to negotiate over border security measures. Republicans have said that they will not pass a package of aid for Ukraine, Israel and Taiwan unless it includes policies to tighten the southern border.

In today’s newsletter, I’ll explain two issues: first, why migration has surged in recent years, and, second, how the current proposals would address it.

When experts try to explain why immigration rises and falls, they talk about “push” and “pull” factors. Push factors are those such as war, famine or economic crisis that cause people to leave their home countries and seek a new home. Pull factors are those that can lure people to a new country, such as an economic boom in that country or a more lax immigration policy. Both push and pull factors have played a role in the surge of migration to the U.S.

Venezuela has descended into disarray in recent years, and Nicaragua’s government has become more repressive. But push factors don’t explain the entire surge — and maybe not even most of it. There have been no recent wars in Latin America, and the region’s poverty rate has been flat.

Pull factors have also been important. During Biden’s presidential campaign, he spoke in much more welcoming tones than not only Donald Trump but also Barack Obama. “We’re a nation that says, ‘If you want to flee, and you’re fleeing oppression, you should come,’” Biden said during a 2020 campaign debate co-hosted by Univision, which has a large audience in Latin America.

Federal policy, even before Biden’s presidency, has played a role, too. A 2015 ruling by a federal judge, for example, made it easier for children to enter the country. (Some of them go on to work dangerous jobs — such as roofing — in the U.S., as The Times has documented.)

Together, these changes have caused many potential migrants to believe that their chances of being able to enter the U.S., and stay, are better than they used to be. “The pull factors are so much of what is happening now,” said Doris Meissner, who was the commissioner of the Immigration and Naturalization Service under Bill Clinton and now works at the Migration Policy Institute.

The Republican border proposals are an attempt to make illegal entry to the U.S. more difficult and, by extension, to change perceptions in Latin America.

Today, migrants who manage to set foot on U.S. soil can often claim asylum. Some genuinely qualify because they have a credible fear of repression in their home countries. Many others do not qualify, but they have learned that claiming asylum allows them to remain in the U.S. for months, if not years, while their case is heard.

Congressional Republicans favor several measures to change this system. One would temporarily shut the border — allowing almost no new asylum claims — if migration flows were to rise above a certain level. Another measure would make it easier for U.S. officials to detain and deport migrants who did not have credible asylum claims. A third would require migrants to have first applied for asylum in countries through which they traveled, like Mexico.

Critics of these ideas have used extreme language to describe them — words like drastic, seismic and severe. But Meissner, the former immigration commissioner, told me that she thought the concerns about the migration surge were “fair” and “legitimate.” The recent rise in undocumented migration has also been drastic, after all.

“The deeper issue here is our immigration laws have not been updated in 30 years,” Meissner said. The ideal solution, she and many other experts believe, would combine stronger border enforcement, more resources to decide cases quickly and clear new ways for people to apply for legal immigration.

Of course, experts have been making the same arguments for years, without Congress acting. The two political parties remain too far apart on the issue to pass any comprehensive bill. But Biden’s push for Ukraine aid — combined with the Republicans’ focus on reducing illegal immigration — could lead to a narrower bill in coming weeks that tightens the border.

  • As the war continues without resolution and many Israeli hostages remain in custody in Gaza, Benjamin Netanyahu’s grip on power seems shakier than ever, Steven Erlanger writes.

  • The Israeli military released more details about the three hostages killed by its soldiers in Gaza. They appeared to have used leftover food to create signs calling for help.

  • Netanyahu said Israel would “fight to the end” as international allies in the U.S., Britain and Germany urge restraint.

  • Israel took reporters to what it said was the biggest Hamas tunnel found since the invasion of Gaza. See inside.

  • The Astal clan is an influential southern Gazan family. More than 100 members have been killed in the war.

Church lunches: After-service meals are key spaces for first-generation Korean immigrants. At Christmas, their children join them.

“The Passing Paisan”: Tommy DeVito, the Giants’ rookie quarterback, is New Jersey’s hometown hero in an era of teams without roots.

M.L.B.: The New York Mets are making a push for Japanese star pitcher Yoshinobu Yamamoto, who ate dinner at owner Steve Cohen’s house over the weekend.

Volleyball: Texas upended No. 1 Nebraska to win the N.C.A.A. national championship, the second title in a row for the Longhorns.

Office parties: The work holiday party is changing — boozy nighttime events are seemingly out and conference room lunches are in. One reason: The pandemic and hybrid work have made employees increasingly resistant to the idea of being away from home in the evenings.