The Trump administration on Tuesday released an aggressive plan to stop illegal immigration, warning that all of the estimated 11 million undocumented immigrants currently living in the United States are subject to deportation at any time.

Two memorandums signed by Homeland Security Secretary John Kelly laid out a series of policies intended to increase immigration enforcement, speed deportations and discourage new asylum seekers. Among the provisions: the hiring of thousands of new border patrol and immigration enforcement agents, the creation of a new office within Department of Homeland Security to work with the victims of crimes committed by unauthorized immigrants, and an expansion of the number of unauthorized immigrants who can be deported through an expedited process.

The practical impact of the orders is not yet clear. Administration officials, in a conference call with reporters on Tuesday, said the moves were not a prelude to mass deportations, which would in any case likely require additional funding from Congress. Many details — including the fate of hundreds of thousands of undocumented immigrants granted temporary protected status by former President Barack Obama — remain unresolved, and some of the new policies will likely face legal challenges.

In the meantime, here is more about what we know — and don’t know — about President Trump’s policies:

Trump meant what he said

The memorandums amount to the clearest evidence yet that Trump plans to make good on his campaign promises to crack down on undocumented immigrants living in the U.S.. And they represent a clear departure from the approach taken by Obama, who after overseeing a surge in deportations early in his administration, worked to reduce them during his final years in office.

The memorandums, which build on the executive orders on immigration Trump signed during his first week in office, drew immediate criticism from pro-immigrant groups. They are likely to be popular with Trump’s core supporters, who made his pledge to build a wall along the Mexican border into a rallying cry during and after the presidential campaign. How the policies will play with the broader public is harder to say: As FiveThirtyEight contributor Dan Hopkins wrote in January, Americans have generally grown more liberal on immigration since 2012, and most oppose mass deportations. But most Americans also oppose “sanctuary cities” that refuse to cooperate with immigration authorities in certain circumstances, and they were divided on Trump’s controversial ban on travel from seven majority Muslim countries.

Trump is retaining, at least for now, one Obama-era policy that has generally proved popular: The 2012 program granting temporary protection to some of the so-called Dreamers, undocumented immigrants brought to the U.S. as children. Trump has called the issue of the Dreamers “a very difficult subject for me,” and Kelly’s memorandum explicitly leaves in place the policy known as Deferred Action for Childhood Arrivals. Its long-term fate, however, remains unclear, as does the fate of the roughly 750,000 participants in the program, some of whose two-year work authorizations are now expiring.

Heightened enforcement

During his first term in office, Obama drew fire from immigration supporters for increasing deportations, particularly along the Mexican border. Later in his administration, however, Obama changed tack, sharply reducing deportations by focusing on immigrants convicted of serious crimes or who had entered the country recently. Undocumented immigrants who were accused only of immigration-related offenses, such as using fake documents in order to work, were usually spared deportation, as were those convicted of traffic violations and other more minor offenses.

Trump and Kelly look set to reverse that shift — and then some. Immigration authorities will continue to focus on immigrants accused of crimes, but the new memorandums substantially expand the list of offenses that are likely to lead to deportation. The administration will prioritize deportation of undocumented immigrants accused — not necessarily convicted — of all “chargeable criminal offenses,” potentially including immigration-related violations. And the memorandums make clear that anyone in the country illegally can be kicked out of the country at any time.

To enact the tough new policies, the DHS will hire 10,000 additional Immigration and Customs Enforcement (ICE) agents. The agency will also look to expand the number of local law enforcement agencies working with the federal government to enforce immigration law. And DHS will release to the public a weekly report on local law enforcement agencies, documenting the number of undocumented immigrants they release from custody — in effect an attempt to shame so-called sanctuary cities.

Immigrants and crime

During the presidential campaign, Trump repeatedly highlighted victims of crimes committed by undocumented immigrants. Tuesday’s memorandums take that approach from the stump into the bureaucracy: The DHS will create a Victims of Immigration Crime Engagement (VOICE) Office that will work with victims of such crimes. “Criminal aliens routinely victimize Americans and other legal residents,” the memorandum reads.

Most research, however, has found that immigrants, including undocumented immigrants, commit violent crimes at lower rates than native-born Americans. That isn’t surprising — non-citizens, even those here legally, face possible deportation if they are convicted of a violent crime, meaning such crimes carry a higher risk than they do for the U.S. born. (The children of immigrants commit crimes at roughly the same rate as other U.S.-born citizens.)

The undocumented population isn’t increasing

Despite Trump’s focus on illegal immigration, the number of undocumented immigrants in the U.S. isn’t increasing — in fact, illegal immigration has slowed to a relative trickle. According to an analysis of Census Bureau data by the Pew Research Center, there were about 11 million people in the U.S. illegally in 2014, the latest data available. That’s down more than a million from 2007. In recent years, the number has been roughly flat — meaning as many undocumented workers are leaving the U.S. as entering it.

Most people in the U.S. illegally have been here a while. Some two-thirds, 66 percent, have been in the U.S. a decade or more, according to Pew’s analysis. Just 14 percent have been here less than five years. In the early 2000s, when illegal immigration was at its peak, those two numbers were roughly equal.

Undocumented immigrants, like immigrants in general, are concentrated in large cities, particularly on the coasts and near the Mexican border. But they live throughout the country — a separate Pew report recently estimated that there are about 20,000 undocumented immigrants in Boise, Idaho, for example. Many, though by no means all, undocumented immigrants work in low-wage sectors such as agriculture and the fast-food industry. (Trump’s initial choice to serve as labor secretary, fast-food CEO Andrew Puzder, drew conservative opposition in part because of his pro-immigration stance. Puzder has since withdrawn his nomination.)

A focus on the Southern border

These memos suggest DHS under Trump views illegal immigration as principally an issue of border crossings from people who live in countries south of the U.S. The memorandums call for the hiring of 5,000 additional Border Patrol agents and require all federal agencies to track any spending of U.S. dollars that benefit Mexico. (Trump could highlight any such spending in his campaign to get Mexico to pay for a border wall.) And they direct immigration enforcement authorities to send people crossing the border back to Mexico — even if they aren’t Mexicans.

This is an outdated view of the nation’s immigration challenges. While Mexicans represent about 52 percent of the undocumented population, according to the Pew Research Center, the number of unauthorized immigrants from Mexico has declined from 6.9 million in 2007 to about 5.8 million as of 2014. A rising share of undocumented immigrants, particularly those who came to the U.S. recently, are from Central America and Asia, and many did not cross the Mexican border to get here. According to data from the Department of Homeland Security, more than half a million people entered the country legally in the 2015 fiscal year and then overstayed their visas. The largest share of them came from Europe, Canada and South America.