Data released by the Department of Homeland Security on Tuesday reinforce the dramatic increase in the number of migrants coming to the United States from and through Mexico. In March, some 92,000 migrants were apprehended at the border, many of whom were seeking asylum in this country. About 58,000 of them were members of families.

Sen. Jeff Merkley (D-Ore.) appeared on CNN on Tuesday evening and explained what he understood to be the cause of the recent increase.

"As far as the surge that we're talking about, that's directly because of Trump,” Merkley said.

“I called up all the folks I’ve been working with on this, what’s going on. They said, well, there’s a couple of small reasons and one big reason,” he continued. “The small reasons are the elections in Guatemala and better bus travel from southern Mexico to northern Mexico. But the big reason? As Trump rants about the border, so many people are saying, ‘I’m in this terrible situation; if I’m going to go, I’d better go now.’ It’s all Trump-generated.”

That latter claim loosely mirrors the change in migration over the past few months. At the end of 2018, the number of families apprehended at the border was higher than in 2016 or 2017, but the overall number of apprehensions tracked with two years prior. In January, as had happened in 2017 and 2018, the number dropped.

In mid-February, Trump announced that he was declaring a national emergency to secure funding to build the wall. Since then, he’s returned to the issue repeatedly and fervently. It’s not clear how much migration to the United States would be affected even if Trump’s national emergency yields substantially more wall construction. Many migrants turn themselves in at border checkpoints to initiate asylum claims. But to an observer, it would be understandable why it might seem like the window for heading north was closing.

Merkley's broader point, though, is interesting. To what extent does Trump bear responsibility for the recent increase in migration — and to what extent are his policies exacerbating the problem?

The economy

Trump frequently claims credit for the strength of the economy, for low unemployment rates and for rising wages. The extent to which he deserves credit is debatable and debated, but it’s a pitch he makes nonetheless.

At times, too, he's linked the strong economy to the increase in migration, as he did at an event over the weekend.

"We're on pace to apprehend more than a million illegal migrants this year,” he said. “A million. They're coming up because of the economy; they're coming up because our laws are so bad from the Democrats.” (Somewhat beside the point here but: Those who seek asylum at border checkpoints are not violating any laws.)

A 2017 report commissioned by Customs and Border Protection found that, among other things, economic incentives were a key motivator for migrants to head to the United States. When the recession hit a decade ago, illegal migration from Mexico slowed dramatically: Less employment damped the appeal of coming to the United States.

It's obviously a good thing to have more people employed and earning higher wages. But it also provides a stronger incentive for economically disadvantaged people to come to the country.

Cuts to foreign aid

Much of the recent increase in migration is a function of people traveling from El Salvador, Guatemala and Honduras through Mexico to reach the United States. In July, speaking at an event, Customs and Border Protection Commissioner Kevin McAleenan described the United States’ successful efforts to work with those countries.

“It might be longer-term, but I don’t think that we should shy away from investing heavily in our partnerships in Central America,” he said. “We’ve got three good partners in the administrations there. If you look at El Salvador, the migration from El Salvador is reduced 65 percent this year. What they’re doing is working, both on the security front and on the economic opportunity front.”

There’s a demonstrated link between crime in El Salvador and migration to the United States, as The Washington Post’s Kevin Sieff reported last week. U.S. aid to El Salvador after there was a surge in minors migrating to the United States in 2014 helped drive down violent crime there — and migration. The aid wasn’t the only factor helping tamp down migration from El Salvador (note that McAleenan points to economics, as well), but experts believe it played a role.

Trump announced last month that he planned to cut aid to all three countries. (Those cuts haven’t been finalized.) Unsurprisingly, there’s concern that such cuts would increase the number of people seeking to migrate to the United States. That would make life much harder for the successor to departing Homeland Security Secretary Kirstjen Nielsen.

On Sunday, Trump announced that until a new secretary is confirmed, the department will be run by McAleenan.

Climate change

One of the unknown factors in the warming climate is the extent to which it will destabilize geopolitics. Several regional conflicts, including in Sudan and (less concretely) Syria, have been linked at least to some extent to climate-change-fueled drought. There’s little question that, over the longer term, rising sea levels and warming temperatures will shift where people can live or make a living. Two reports in recent weeks have linked the current migration crisis to changes in agriculture that stem from the warming climate.

A “PBS NewsHour” report found decreases in rainfall and warming temperatures were eradicating corn crops in Honduras. One farmer, Don Alfredo Monge, expressed desperation at not being able to feed his family, saying “we will have to get out of here.” He said he worried about Trump (whom he described as “tough”).

“I worry,” he said, “but the hunger forces me to go.”

The New Yorker had a similar report on agricultural production in Guatemala. It provided an insightful look at how the inability to grow crops overlapped with migration and the surge in asylum claims.

“Changing weather patterns were forcing them to purchase fertilizers, extra compost, and pesticides. The growing season had also contracted, meaning most harvests were selling at the same time, driving down the price. One potato farmer, a seventy-five-year-old with two children in the U.S., had given up on trying to grow anything. ... The son of another farmer had left for the U.S. three months earlier, taking his nine-year-old daughter with him. ‘How else was he going to get across the border?’ the father said. ... ‘The ticket is travelling with a kid,’ he added. ‘They try to cross the border with their children because they know they’ll get released when they seek asylum.’”

There’s nothing that can be done over the short term to address the changing climate (though, of course, the United States and other countries could give aid to offset the damage done by changing weather patterns). There’s probably not much that can be done over the long term to change the effects that are being felt right now, either.

But Trump’s long-standing rejection of climate change and his decision to have the United States step back from addressing the problem will probably increase the long-term effects of global warming. That will probably mean more “climate refugees,” people forced to leave their communities because of increased warmth or other shifting patterns like those identified above.

That’s very much a long-term problem. But it speaks to the original point alluded to by Merkley. For all of Trump’s insistences that not enough is being done to address the increase in migrants, Trump himself bears some responsibility for the moment — and, almost certainly, for higher migration in the medium and long terms.