During his first term as president, Donald Trump tested the limits of how he could use the military to achieve policy goals. If given a second term, the Republican and his allies are preparing to go much further, reimagining the military as an all-powerful tool to deploy on U.S. soil.

He has pledged to recall thousands of American troops from overseas and station them at the U.S. border with Mexico. He has explored using troops for domestic policy priorities such as deportations and confronting civil unrest. He has talked of weeding out military officers who are ideologically opposed to him.

Trump’s vision amounts to a potentially dramatic shift in the role of the military in U.S. society, carrying grave implications for both the country’s place in the world and the restraints that have traditionally been placed on domestic use of the military.

As Trump’s campaign heads into its final stretch against Democratic Vice President Kamala Harris, he is promising forceful action against immigrants who do not have permanent legal status. Speaking in Colorado on Friday, the Republican described the city of Aurora as a “war zone” controlled by Venezuelan gangs, even though authorities say that was a single block of the Denver suburb, and the area is safe again.

“I will rescue Aurora and every town that has been invaded and conquered,” Trump said at the rally. “We will put these vicious and bloodthirsty criminals in jail or kick them out of our country.”

In an interview aired Sunday on Fox News Channel, Trump was asked about the potential of “outside agitators” disrupting Election Day and he then pivoted to what he called “the enemy from within.”

“I think the bigger problem is the enemy from within,” Trump said. He added: “We have some very bad people. We have some sick people, radical left lunatics. And I think they’re the big — and it should be very easily handled by, if necessary, by National Guard, or if really necessary, by the military, because they can’t let that happen.”

Trump has repeatedly invoked the phrase “enemy from within” in recent speeches. On Saturday, he used it to refer to Rep. Adam Schiff, D-Calif., a prominent Trump critic who oversaw the congressional investigation that led to Trump’s first impeachment. Schiff is now running for the Senate.

The former president and his advisers are developing plans to shift the military’s priorities and resources, even at a time when wars are raging in Europe and the Middle East. Trump’s top priority in his platform, known as Agenda 47, is to implement hardline measures at the U.S.-Mexico border by “moving thousands of troops currently stationed overseas” to that border. He is also pledging to “declare war” on cartels and deploy the Navy in a blockade that would board and inspect ships for fentanyl.

Trump also has said he will use the National Guard and possibly the military as part of the operation to deport millions of immigrants who do not have permanent legal status.

While Trump’s campaign declined to discuss the details of those plans, including how many troops he would shift from overseas assignments to the border, his allies are not shy about casting the operation as a sweeping mission that would use the most powerful tools of the federal government in new and dramatic ways.

“There could be an alliance of the Justice Department, Homeland Security and the Department of Defense. Those three departments have to be coordinated in a way that maybe has never been done before,” said Ron Vitiello, who worked as the acting director of Immigrations and Customs Enforcement under Trump.

While both Democratic and Republican presidential administrations have long used military resources at the border, the plans would be a striking escalation of the military’s involvement in domestic policy.

Advocates for human rights and civil liberties have grown alarmed.

“They are promising to use the military to do mass raids of American families at a scale that harkens back to some of the worst things our country has done,” said Todd Schulte, president of FWD.us, an immigration advocacy organization.

In Congress, which has the power to restrict the use of military force through funding and other authorizations, Republicans are largely on board with Trump’s plans.

“The reason I support Donald Trump is he will secure the border on Day 1. Now that could be misinterpreted as being a dictator. No, he’s got to secure the border,” said Rep. Joe Wilson, R-S.C., a member of the House Armed Services Committee.

Many Republicans argue that Trump’s rhetoric on immigration reflects reality and points to the need for military action.

“There is a case that this is an invasion,” said North Carolina Sen. Ted Budd, a Republican on the Senate Armed Services Committee. “You look at 10 million people, many of which are not here for a better future, and, unfortunately, it’s made it necessary. This is a problem that the Biden administration and Harris administration have created.”

Still, Trump’s plans to move military assets from abroad could further inflame tension within the GOP between those hawkish on foreign policy and Republicans who promote Trump’s brand of “America First” isolationism.

Republican Rep. Mike Rogers of Alabama, chairman of the House Armed Services Committee, insisted Trump would not move active-duty troops to the border, even though Trump’s platform clearly states he would.

In the Senate, where more traditional Republicans still hold sway, Mississippi Sen. Roger Wicker, the top Republican on the Armed Services Committee, issued a statement encouraging the Department of Defense to assist with border security, but adding that the effort “needs to be led by the Department of Homeland Security.”

Trump’s designs for the military may not stop at the border.

As Trump completes a campaign marked by serious threats to his life, his aides already made an unusual request for military aircraft to transport him amid growing concerns over threats from Iran.

During his first term while riots and protests against police brutality roiled the nation, Trump also pushed to deploy military personnel. Top military officers, such as then- Gen. Mark Milley, resisted those plans, including issuing a memo that stressed that every member of the military “swears an oath to support and defend the Constitution and the values embedded within it.”

Trump’s potential actions would likely require him to invoke wartime or emergency powers, such as carrying out mass deportations under the Alien Enemies Act, a 1798 law, or quelling unrest under the Insurrection Act, an 1807 law that allows a president to deploy the military domestically and against U.S. citizens. It was last used by President George H.W. Bush in 1992 during rioting in Los Angeles after police officers beat the Black motorist Rodney King.

Ahead of a potential second term for Trump, Democrats in Congress tried to update presidential powers like the Insurrection Act but found little success.

That’s left them instead issuing dire warnings that Trump now has fewer guardrails on how he could use the military. He has shown an ability to bend institutions to his goals, from a Supreme Court willing to reconsider long-standing interpretations of presidential powers to a military scrubbed of officers and leaders likely to push back on his plans.

Sen. Richard Blumenthal, D-Conn., who introduced legislation to update the Insurrection Act, said the plans “illuminate Donald Trump’s total misunderstanding of the United States military as a force for national defense, not for his personal preferences to demagogue an issue.”

But Rep. Dan Crenshaw, R-Texas, underscored how many in his party have grown comfortable with deploying the military to confront illegal immigration and drug trafficking.

“Whatever fixes the border, I think we’re OK with,” he said.