Immigration analysts say President Donald Trump’s executive actions Wednesday to combat illegal immigration signify his intent to strip away impediments imposed by his predecessor and enforce existing laws more strictly.

“The executive orders signed today reflect the administration’s understanding that there is more to immigration security than just building the wall,” Jessica Vaughan, the director of policy studies at the Center for Immigration Studies, said in an interview with The Daily Signal.

Trump began an effort to dramatically reshape immigration policy, signing a pair of executive actions to enhance enforcement of the law and begin construction of a wall across the southern border.

“The secretary of homeland security, working with myself and my staff, will begin immediate construction of a border wall,” Trump said, flanked by Vice President Mike Pence and Homeland Security Secretary John Kelly.

The presidential directives include withholding funds from so-called sanctuary cities that limit their cooperation with federal immigration authorities, increasing the use of detention centers, and endorsing the hiring of additional Border Patrol and interior enforcement agents.

The measures, some of which will require congressional support, represent a substantial policy shift from President Barack Obama, Vaughan and other immigration analysts told The Daily Signal.

How to Build a Wall

In announcing his actions at the headquarters of the Department of Homeland Security, Trump expressed surprise at how much he can do on his own, and within existing law.

For starters, immigration policy experts agree the Trump administration at least can begin “immediate” construction of the border wall, based on previous authority in a 2006 law signed by President George W. Bush. Called the Secure Fence Act, it mandated a minimum of 700 miles of “physical barrier” on the nearly 2,000-mile southern border.

The 2006 law called specifically for double-layered fencing, but a little more than a year later Congress amended it to allow Border Patrol the leeway to decide what types of barriers were appropriate in various regions.

The amended law never was fully implemented (only 36 miles of fencing is double-layered), nor did it set a deadline for the fencing or other barriers to be built. This means Trump could pick up where Bush left off by redirecting already-authorized federal funds.

But Trump will need Congress to approve additional funding to do the bulk of the building.

The president has estimated the cost of the wall to be $8 billion to $12 billion. Other estimates have put it at $25 billion. The Trump administration also must follow a decades-old border treaty with Mexico that limits where and how structures can be built.

“There is nothing shovel-ready here,” said Theresa Cardinal Brown, director of immigration policy at the Bipartisan Policy Center and a former policy adviser at the Department of Homeland Security.

“This will take a bit of time, and require more money, logistics planning, and manpower,” Brown told The Daily Signal in an interview. “We will see over the course of the coming months what actually happens, because the realities of doing some of this stuff are much more complex than saying, this is what I want to do.”

Enforcement Policy Changes

Shawn Moran, vice president for the National Border Patrol Council, the largest union for Border Patrol officers, told The Daily Signal that his organization has recommended to the Trump administration that they undertake a review of border sectors to determine the infrastructure appropriate for each place.

Moran downplayed the impact of a border wall, conceding that it “may not stop” the most prevalent form of illegal immigration today: Central American children and families fleeing violence, corruption, and poverty willingly surrender to Border Patrol agents and plead for asylum.

But some of Trump’s other priorities described in his executive orders will speed up the processing of cases and deter future illegal immigration, Moran said.

“We are looking forward to policy changes that will take place, and we think that is where the real effect will be seen in terms of immigration enforcement and border security,” he said.

To step up deportations and detentions, Trump announced that he is directing the Department of Homeland Security to bring back a local enforcement program called Secure Communities that drew some sharp criticism. Bush started the program and Obama ended it.

Under Secure Communities, federal immigration agents asked law enforcement agencies to keep illegal immigrants in custody for an extra 48 hours than normal so federal authorities could pick them up and deport them. These requests were known as detainers.

Critics of the program said it violated illegal immigrants’ civil rights, and did not differentiate between their being arrested initially for low-level or serious offenses. Many local jurisdictions stopped complying with the program, fearing they would be sued by advocacy groups.

In November 2014, the Obama administration replaced Secure Communities with the Priority Enforcement Program (PEP), which is less demanding of local authorities.

The Obama administration also narrowed those targeted for deportation to focus on illegal immigrants considered threats to national security and public safety, who likely have been convicted of a felony. Other priorities for deportation included individuals convicted of multiple misdemeanors, as well as recent arrivals.

Trump has said that he too will prioritize deporting criminal illegal immigrants. But his executive order broadens Obama’s enforcement targets and calls for deportations based on any criminal conviction or commission of an act that “constitutes a chargeable offense.” Other targets include individuals who have received a final order to leave the country but haven’t done so, and those who have engaged in fraud or willful misrepresentation before a government agency.

Challenges Ahead

Some of the other directives detailed in Trump’s executive orders are less specific and will require agencies to work out a plan.

For example, the sanctuary city order doesn’t take any action and doesn’t specify what types of funding the executive branch would withhold from cities that shield illegal immigrants from deportation.

Immigration analysts say that depending on what the administration ultimately does, sanctuary states and localities likely will challenge Trump in court, given Supreme Court rulings that limit the federal government’s ability to make grants conditional on specific policies.

“It’s very likely states and jurisdictions will fight those policies, and you can expect to see a lot of litigation,” Faye Hipsman, a policy analyst at the Migration Policy Institute, said in an interview with The Daily Signal.

One of the first threats to challenge Trump’s policy came from Kevin de Leon, a Democrat who leads the state Senate in California. That state strictly limits the situations in which local agencies will help the federal government take custody of those it seeks to deport.

Other objectives that Trump describes in his executive orders include prioritizing border prosecutions for those who repeatedly cross the border illegally, or are engaged in drug smuggling, weapons trafficking, and other criminal activity.

In addition, Trump calls for ending “catch and release,” in which the Border Patrol apprehends somebody and quickly returns him or her to the other side of the border with no penalty.

The Obama administration used this protocol to free immigrants seeking asylum while they await a hearing with an immigration judge, who determines if they can stay in the country.

“Ending catch and release would require a huge use of detention,” Hipsman said. “Because court backlogs are so long, you would need to keep immigrants in detention for months or years.”

But Trump could face roadblocks in using detention more. A federal appeals court in 2015 sharply limited the ability of immigration authorities to detain children who enter the country illegally.

Meanwhile, Congress would have to approve funding for another major Trump proposal: tripling the number of U.S. Immigration and Customs Enforcement agents who focus on deporting those in the country illegally, and hiring an additional 5,000 Border Patrol agents.

The Border Patrol has faced challenges fulfilling hiring goals mandated by Congress. Since 2001, the U.S. has more than doubled the ranks of the Border Patrol, which now has nearly 20,000 agents.