“He obviously wants everyone to believe he’s talking about some mass roundup, which is just not possible,” immigration attorney Matt Cameron said of Trump, “both because of resources and because of due process.”

“Next week ICE will begin the process of removing the millions of illegal aliens who have illicitly found their way into the United States,” he tweeted. “They will be removed as fast as they come in.” An administration official later told the Associated Press that the effort would target people who have received final orders of deportation. There are more than 1 million people living in the United States with final deportation orders, among an undocumented population of about 11 million.

The genuine fear, coupled with the artificial threat, coming at a time of maximum insecurity for immigrants in the United States, has put immigrant rights’ groups in a bind. They are being careful in their responses to Trump’s tweet, trying to avoid creating panic, while also trying to equip people with resources needed to defend themselves legally. Adonia Simpson, director of the Family Defense Program at the Miami-based Americans for Immigrant Justice, said her group was considering whether to host a know your rights training, noting that, in her experience, immigrants tend to be afraid to go out and access legal resources at times like these. The National Immigrant Justice Center, for its part, has been circulating know your rights information online.

Simpson described people with final deportation orders as the “lowest hanging fruit” of the immigration system. ”The easiest population to go after would be individuals that have final orders of removal and are perhaps going to check in at their local ICE offices,” she said. (People with final orders of removal are sometimes allowed to stay in the United States as long as they periodically check in with Immigration and Customs Enforcement, often because the agency lacks the resources to deport them, they have strong family ties in the country, or there is no other country willing to take them in.)

Speaking to reporters on Tuesday, Trump linked his announcement of a mass roundup to recent talks with Mexico and Guatemala to keep asylum-seekers from reaching the United States, which is vastly different from removing people with final deportation orders from the country. This is yet another indication that Trump’s tweet — issued the night before his official 2020 campaign launch — was about appealing to a nativist base rather than an actual policy.

Another possibility is that Trump was referring to the rumored expansion of expedited removal, a program that currently allows ICE to quickly deport people within 14 days of their entry to the United States, if they’re caught within 100 miles of the border. “To be totally blunt, I don’t think Trump is capable of that level of nuance,” said Aaron Reichlin-Melnick, a policy analyst at the Migration Policy Institute.

By all measures, a plan to deport “millions” of people is an astounding exaggeration — even beginning to deport millions, as Trump pledged ICE would do, stretches the truth to a breaking point. As Sarah Pierce, an analyst at the Migration Policy Institute, pointed out on Twitter, ICE has deported an average of 90,000 people from the interior of the United States in recent years. The largest number of people ICE deported overall — from the interior, as well as recent border crossers — was about 420,000 people in 2012.

In response to a question about Trump’s tweet, ICE sent a statement that referred to interior enforcement. “ICE will continue to conduct interior enforcement without exemption for those who are in violation of federal immigration law,” the statement reads. “This includes routine targeted enforcement operations, criminals, individuals subject to removal orders, and worksite enforcement.”

Regardless of what Trump was referring to, or if such a plan to deport immigrants actually exists, ICE is not actually capable of such a large-scale deportation operation, immigration lawyers and analysts say.

There are about 5,000 officers in Enforcement and Removal Operations, or ERO, an arm of ICE, who carry out deportations. From a basic staffing perspective, that’s not enough people to work to arrest and deport millions of people. Even if ICE transferred personnel from Homeland Security Investigations, the arm that looks into criminal activity and trafficking, to ERO, there would still be a shortage of officers.

“The only way they could really actually do this is to reassign people from HSI without actually going after people with serious criminal records,” said Cameron, who noted that the majority of immigrants with final deportation orders don’t have criminal records. “Potentially they’re giving up serious security investigations,” he added, referring to ICE. “We can talk about the necessity of those investigations, but at least on paper, that’s what they justify their existence with.”

ICE did not respond to a question about whether it would transfer personnel from HSI to ERO.

Another factor that makes it impossible for ICE to effectuate the plan is the lack of available bed space. Deportees don’t go straight from custody to a foreign country, but are generally detained first; there are about 50,000 beds in immigration detention centers around the country. Then there are basic logistics. To track down people with final deportation orders, ICE would probably look them up at their last known address, which, in most cases, is likely not their current address, Cameron said. Immigrants with final deportation orders often don’t have passports, and ICE would have to engage in a monthslong process to obtain travel documents for the people it intends to deport.