SAN ANTONIO, Texas ― The plummeting number of unauthorized crossings from Mexico may allow the Trump administration to focus more energy on deporting undocumented immigrants already living here, former immigration officials say.

Since President Donald Trump took office, the number of unauthorized crossings have dropped to a 45-year low. If those numbers stay down, it could mean that Immigration and Customs Enforcement will see a sizable chunk of its workload evaporate, even as the White House demands the agency hire another 10,000 agents.

With less work at the border and a mandate to enforce immigration law more aggressively, ICE’s former deputy director for congressional relations, Kate Christensen Mills, says agents will increasingly target people with stronger ties to the United States.

“If you’re going to have a decrease of people coming across the border, you’re going to have an increase in interior enforcement,” Mills said, speaking at a panel at the Border Security Expo Tuesday. “You’re also going to see an increase in detention.... Some are going to have ties to the community. So processing them is going to take a little bit longer.”

Bureaucratic constraints will continue to undermine Trump’s efforts to boost deportations, Mills added. The lack of judges in immigration courts has contributed to a years-long backlog. The immigrant detention system has run over capacity in recent months. And the White House has proposed to gut the State Department’s budget by around 30 percent, despite the fact that ICE heavily relies on the department to secure the travel documents deportees need to be removed from the country.

But if illegal border crossings keep dropping, Mills expects ICE to detain and deport more people with long ties to the United States and without criminal records ― exacerbating a trend the Trump administration has established within weeks of his inauguration.

“There’s only so many criminal aliens,” Mills said. “So ICE is going to go after people living illegally in the United States. And some of them will not be criminal aliens.”

ICE distinguishes between two types of deportees: those caught while trying to cross the border illegally and those arrested in the interior of the country. For decades, those caught at the border made up the majority of removals, though not everyone was formally deported by ICE.

Since 2014, however, deportations from the border zone have become increasingly complicated because most of the people crossing come from Central America rather than Mexico. In many cases, the Border Patrol itself can return Mexican nationals arrested for jumping the border within 48 hours and without getting ICE involved.

The Border Patrol can’t fly people to countries beyond Mexico, however. And people from El Salvador, Guatemala and Honduras are often fleeing violence and routinely ask for asylum or other humanitarian exemptions from deportation. That kicks off a lengthy legal process that puts the case in ICE’s hands.

“If these declining numbers are sustained and the era of large migration from Central America has in fact ended, yes ― I expect you’ll see a big uptick in interior removals,” John Sandweg, who headed ICE for part of Obama’s second term, said.

Doris Meissner, a former commissioner of the Immigration and Naturalization Service, expected a less drastic effect, pointing out that in order for ICE to take full advantage of the change, the agency would have to relocate people previously tasked with working at the border.

“Unless you start detailing all kinds of people into the interior area, it’s not an entirely transferrable workforce,” Meissner, who now serves as a fellow with the non-partisan Migration Policy Institute, told HuffPost. “But it probably is true that it allows for more resources to be directed toward people in the interior of the country.”

Many immigration analysts already expected a pronounced jump in the level of interior deportations. Within weeks of taking office, Trump eliminated Obama-era deportation policies that had required ICE to focus its attention on recent border crossers, people with criminal records and those who’d been deported before.

Under a January executive order, Trump issued a new set of deportation priorities that include virtually the entire undocumented population of 11 million – though in practice, people who are arrested by local law enforcement or who’ve had prior orders of deportation are the most likely to be detained by ICE.

In his first year in office, Obama deported nearly 238,000 people from the interior of the country. Thanks largely to those deportation priorities, first implemented in 2011, that number dwindled every year of his presidency. Last year ended with 65,332 interior deportations ― about a quarter of ICE’s total deportations, with the rest coming from the border zone.