As it became clear on election day that Republicans would lose the House of Representatives, House Homeland Security Committee Democrats posted a three-word message on social media to Markwayne Mullin, who leads the agency: "clear your calendar." The next day, Mullin posted a three-word message of his own: "Deportations will continue."

After affordability and the Iran war, immigration was a defining issue in the midterm elections, and now that Democrats won majorities in the House and Senate, they plan to increase agency oversight and attempt to rein in the Trump administration's aggressive immigration enforcement policies. Come January, Democrats will control every House seat along the U.S.-Mexico border. But while they will have wider leeway to investigate alleged wrongdoings of the last two years, how much they can advance their immigration agenda will likely depend on how much Republicans will collaborate with them. Any advances would also require the approval of President Trump, who on Friday appointed Stephen Miller, the architect of many of his administration's most stringent immigration policies, as his new chief of staff.

Democrats have already started outlining their goals for next year and preparing to staff up. Job listings posted last week seek investigators, lawyers and law clerks whose duties would include immigration.

Rep. Robert Garcia (D-Long Beach), who is poised to lead the House Committee on Oversight and Government Reform, said one of his major focus areas would be the Department of Homeland Security and abuses by immigration agents. Garcia specifically named former Homeland Security Secretary Kristi Noem and her advisor Corey Lewandowski, saying they would face accountability and justice. "When people are being kidnapped and detained, thrown to the ground, arms broken, people snatched up on their way to immigration appointments that we the government gave them, that's inhumane, it's wrong, and I think the American public — regardless of party — are sick of it," Garcia said Wednesday at a news conference in Huntington Beach. Rep. Bennie Thompson of Mississippi, the top Democrat on the House Homeland Security Committee, sent a letter to Mullin the same day demanding that his department preserve all documents, including emails and contracts, and prepare to hand them over.

Sen. Richard Blumenthal of Connecticut, the top Democrat on the investigations subcommittee of the Committee on Homeland Security and Governmental Affairs, made a similar request.

Blumenthal said he has written Homeland Security leaders more than a dozen times and received no records.

But that was when Republicans controlled the subcommittee. Last week, he wrote, "Please also note that failure to voluntarily produce the requested records and information by January 4, 2027, will leave the Subcommittee with no choice but to consider alternative measures to obtain compliance." Republicans, too, have begun preparing for the coming power shift.

House Majority Leader Rep. Steve Scalise (R-La.) told GOP committee chairs to identify possible targets of Democratic scrutiny and to consider how recent Supreme Court decisions will factor into oversight moving forward.

"They will use their oversight authorities to harass the President, his family, cabinet officials, and they will seek to destroy our allies," Scalise said in a letter Thursday. "You will all be a key line of defense in this fight, and we must maximize our remaining days in power to prepare for what is coming."

Planning by companies that operate immigrant detention facilities for Immigration and Customs Enforcement is already factoring in Democratic control of Congress.

During a call with investors on Thursday, Lucibeth Mayberry, the chief executive of CoreCivic, was asked whether election results will affect future sales of privately run detention facilities to Homeland Security.

"We would urge the ICE administration to move quickly," she said, adding that "there's no reason to wait." Asked if the election results would affect ICE activity, Mayberry did not anticipate any immediate change, noting that ICE has already increased enforcement and expanded the number of detainees, currently around 69,000. While immigration enforcement is unlikely to change, the administration signaled an openness to modifying some tactics.

In a statement on social media the day after the election, Vice President JD Vance said he’s “open to the idea that we should change enforcement — by focusing more on businesses that hire illegal labor, for instance.”Trump, speaking to reporters Friday in Florida, said that immigration is one Democratic-led initiative he could get behind. But in tapping Miller as his chief of staff, Trump signals a desire to continue the aggressive tactics of the last two years, said Sen. Alex Padilla (D-Calif.). "Voters demand lower costs, an end to the chaos, and a government that works for them," he wrote in a statement Friday.

"I know Trump heard them, but sadly and predictably, he’s choosing to double down, handing the keys of the West Wing to the man most responsible for this Administration’s failures and most harmful policies." A majority of voters support a path to citizenship for longtime immigrants, banning immigration agents from wearing masks, mandating use of body cameras and limiting use of force, according to a poll by the Los Angeles-based analytics firm BSP Research of more than 10,000 midterm voters. Most poll respondents also support redirecting billions of dollars appropriated by Congress for immigration enforcement to other government programs.

Rep. Pramila Jayapal of Washington, the top Democrat on the House Judiciary Subcommittee on Immigration Integrity, Security and Enforcement, acknowledged Trump may not sign a comprehensive immigration reform bill. But she said Trump would be going against the will of American voters. "Especially now that Stephen Miller has become the chief of staff, we will have to pass our comprehensive reforms on immigration and send it to Trump’s desk," she said.

"If he and Stephen Miller want to veto it and continue their cruel sweep, we can hold them accountable, not give them any money for it and show them what a real solution looks like." Blumenthal said the investigations subcommittee will focus not just on enforcement, but alleged corruption, such as the airplanes reportedly purchased at inflated prices from a political donor to Noem when she was Homeland Security secretary.

Blumenthal said he's hopeful that a handful of Republican senators up for reelection in 2028 will work with Democrats on legislation that would require immigration agents to wear badges and identify themselves, bar them from wearing masks, and hold them to account when they kill people. "We don't have 60 Democratic votes," he said, referring to the threshold needed to stop a filibuster, "but I'm hopeful Republicans will insist on decency and humanity."

Chris Tausanovitch, a political science professor who studies Congress and the federal government, said it's very unlikely Democrats can overcome a presidential veto, which requires two-thirds votes in both chambers.

That leaves the budget process as their main vehicle for change, Tausanovitch said. Trump could veto a budget passed through a simple majority, but he'd face the prospect of a government shutdown.

Similar budget negotiations have taken place in the second half of the second term of recent presidents, he said. The party that won the midterms usually got something they wanted by making a narrow change in the budget. But Trump is unlikely to give ground on immigration.

"Part of the problem is that, unlike before the Biden administration, when there were a lot of proposals to pair citizenship for undocumented people with border security in some sort of grand compromise, the Republicans have gotten a lot of what they wanted on immigration," he said. "There’s not an opportunity for a bargain like that, because the enforcement part of the bargain is already done." Instead, Tausanovitch said, Democrats will probably focus their political capital on healthcare and affordability — issues where they have the greatest popularity and can create a winning message for 2028.