President-elect Donald Trump is expected to kick off a slew of executive actions related to immigration after his inauguration ceremony, beginning as soon as Monday.

Since the early days of the 2024 presidential campaign, Trump has vowed to begin his second term with both new and old efforts to curb legal migration and deport those who are in the U.S. without legal status.

Last night during a rally in Washington D.C., Trump said he plans to sign executive orders quickly and launch “the most aggressive, sweeping effort to restore our borders the world has ever seen.”

“Very soon, we will begin the largest deportation operation in American history,” he added.

Incoming Trump border czar Tom Homan also said large-scale raids to deport and detain those without legal status are set to begin as soon as Tuesday, focusing on people considered a security or safety threat.

“While we hope for the best, we take Trump at his word. We are prepared to fight back against any cruel or violent attacks on immigrant communities in the U.S. or those fleeing to this country in search of safety and refuge,” said Kerri Talbot, co-executive director of the Immigration Hub, an advocacy organization.

The U.S. had seen an increase in border crossings under the Biden administration, at times reaching all-time highs. But Customs and Border Protection’s recent numbers have shown a sharp decrease in unauthorized apprehensions in the past six months.

Trump campaigned on border security promises, and he and his allies argue that his electoral win is an endorsement of his upcoming efforts on the issue. Republicans criticized Biden’s immigration policies, and lawmakers voted to impeach Biden’s Homeland Security Secretary Alejandro Mayorkas.

Still, the latest NPR/PBS News/Marist poll finds that Americans are evenly split on whether to mass deport people who are in the U.S. without legal status — though divisions fall along party lines.

With Republican control of the White House, Senate and House, Trump’s immigration policies are also a key priority to push through Congress.

Here are some of his promises:

Declare a national emergency, which would unlock federal funding and other authorities to help him carry out plans to secure the border

These efforts may take time

Although Trump has reiterated these promises for over a year, they may take weeks or months to implement. Several actions will likely be the subject of legal challenges or need Congress to mobilize new funding that Trump currently does not have.

“We get into the big question marks. He’s talked about using, expanding, detention facilities. That will almost certainly happen,” Andrew Selee, president of the nonpartisan Migration Policy Institute, said in an interview with NPR’s Morning Edition.

“But whether he’ll be able to use military bases or not, or other federal facilities — and whether he will try and use the military itself, and that would require going back to the Alien and Sedition Act of 1798, and that will almost certainly be litigated in the courts.”

In fact, even quickly scaling operations might be difficult for the new administration. An NPR investigation last year found that U.S. Immigrations and Customs Enforcement, the agency responsible for removals, struggled to scale up to Trump’s immediate demands during his first term, which included attempts to increase deportations.

Congress must also provide the Department of Homeland Security and other agencies with the funding to execute the policies.

In their final budget request, the Biden administration asked for $19 billion to fund additional personnel, facilities, repatriation capabilities, and other enforcement resources along the southwest border.

Lawmakers are expected to take up border security funding as a part of a bigger budget-related measure later this year.