President Trump today signed executive orders threatening federal funding for so-called sanctuary cities and enabling further construction of what White House Press Secretary Sean Spicer called “a large physical barrier” along the U.S.-Mexico border, otherwise known as the border wall.

Trump is going on “an immigration blitz” this week, as the Washington Post reported. Trump’s executive order targeting sanctuary cities, a term for those that have vowed not to criminalize undocumented immigrants based on citizenship status, goes back to a promise he made on the campaign trail. In September, during his highly-anticipated speech on immigration, Trump vowed to block funding for sanctuary cities.

“Cities that refuse to cooperate with federal authorities will not receive taxpayer dollars, and we will work with Congress to pass legislation to protect those jurisdictions that do assist federal authorities,” Trump said.

Continuing to push the narrative that undocumented immigrants are violent criminals protected by sanctuary city policies, Trump’s executive order will create a “victim’s advocacy office” for victims of crimes committed by undocumented immigrants.

Undocumented immigrants are far less likely to commit crimes than people born in the United States.

Most sanctuary cities offer little more than statements of solidarity, which is why advocates are taken aback by Trump’s insistence on pulling federal funding from such cities, which include Los Angeles and New York.

Officials from self-proclaimed sanctuary cities pushed back against Trump’s executive order. New York State Attorney General Eric Schneiderman issued a statement saying, in part, that Trump “lacks the constitutional authority” to cut funding to sanctuary cities and that “local governments, seeking to protect their immigrant communities from federal overreach have every right to do so.”

Former Immigration and Customs Enforcement (ICE) Director Sarah Saldaña told Congress last year that more than 200 state and local jurisdictions have policies that call for not honoring ICE detention requests. But the criminal justice system and the immigration detention system are so intertwined that ICE and police departments often work together for joint enforcement and removal operations. This is true even in immigrant-friendly cities like Los Angeles, where the city’s police department has said it will not work with ICE, though Los Angeles County does.

Trump’s other executive order on Wednesday directs the Department of Homeland Security (DHS) to begin additional construction on the U.S.-Mexico border, including a mandate to increase Border Patrol staff by 5,000 to handle the continued influx of Central American asylum seekers fleeing violence in their countries of origin.

“Building a wall” has been a central tenet of Trump’s immigration plan, but the specifics of how this will be done—and who will pay for it—remain murky. Trump has insisted that Mexico will pay for the wall, though Mexican President Enrique Peña Nieto recently said “that Mexico of course will not pay.” American taxpayers could have to shell out between $15 billion and $25 billion for Trump’s wall expansion.

Politico recently reported that Republicans may include border wall funding in a “must-pass spending bill” that would need to be enacted by the end of April. However, a new law wouldn’t be needed to fund the border wall.

“Republican leaders could use a 2006 law signed by former President George W. Bush that authorized the construction of 700 miles-plus of ‘physical barrier’ on the southern border. The law was never fully implemented and did not include a sunset provision, allowing Trump to pick up where Bush left off,” according to Politico.

Trump is following President Obama’s lead. Obama reinforced the border in ways that Trump is only bolstering under his proposals. Trump’s wall is effectively already in place. According to Obama’s own administration, the DHS dedicated unprecedented resources to Southwest border security. Obama added 3,000 Border Patrol agents along the Southwest border and doubled border fencing, unmanned aircraft surveillance systems, and ground surveillance systems.

None of Obama’s “border security” measures stopped the tens of thousands of women and unaccompanied children migrating to the United States in 2014 as asylum seekers fleeing violence in Central America. As immigrant rights advocate Erika Almiron told Rewire in October, “There is no deterrence for people who are running for their lives.”

Trump’s moves to start additional construction on the border wall and take action against sanctuary cities will not be his last moves on immigration. He will reportedly order a temporary ban on refugees and suspend visas for citizens of Syria and six other predominantly Muslim countries. Spicer said Wednesday that Trump will expand the detention system, already rife with human rights violations and medical negligence, to more “cheaply” detain immigrants.

Trump will reinstate the highly controversial Secure Communities (S-Comm) program put into place by President George W. Bush and escalated under President Obama. S-Comm was ended in 2014 and swiftly replaced by the Priority Enforcement Program (PEP), which is essentially the same program.