President Trump is planning to sign executive orders Wednesday enabling construction of his proposed border wall, and targeting cities where local leaders refuse to hand over illegal immigrants for deportation, part of a multi-day rollout of his long-promised crackdown on illegal immigration, officials familiar with the decision said Tuesday.

“Big day planned on NATIONAL SECURITY tomorrow,” Trump wrote on Twitter late Tuesday. “Among many other things, we will build the wall!”

The moves represent Trump’s first effort to deliver on perhaps the signature issue that drove his presidential campaign: his belief that illegal immigration is out of control and threatening the country’s safety and security.

On Wednesday, Trump plans to speak to a town hall of employees at the Department of Homeland Security’s headquarters in Washington, where he is expected to sign the orders. The effort to crack down on what are known as sanctuary cities will resonate with the Republican base, which has long criticized local officials who refuse to cooperate with federal immigration authorities. Later this week, officials said, the president plans to sign other orders restricting immigration and access to the United States for refugees and some visa holders from Iraq, Iran, Libya, Somalia, Sudan, Syria and Yemen, although the exact timing was being arranged late Tuesday and was subject to change. Residents from many of these places are already rarely granted U.S. visas.

Senior Trump advisers such as chief strategist Stephen K. Bannon and attorney general nominee Jeff Sessions were deeply involved in the extended debate about the orders, said several people familiar with the discussions. These people emphasized that the week’s actions are intended to start fulfilling Trump’s campaign promises on immigration and bring Republicans behind Trump on the issue, one day before he speaks at Thursday’s congressional Republican retreat in Philadelphia. These people spoke on the condition of anonymity because the executive orders were still being finalized.

EXTENT OF CRACKDOWN UNCLEAR

President Trump plans to speak to a town hall of employees at the Department of Homeland Security’s headquarters in Washington, where he is expected to sign the orders cracking down on immigration.

Although Trump’s immigration efforts this week are widely seen inside the White House as a victory for the self-described populist wing of his inner circle – which includes Bannon, Sessions and top policy adviser Stephen Miller – there are ongoing discussions about just how far to go on some policies, in particular the Deferred Action for Childhood Arrivals program, also known as DACA. The 2012 initiative has given temporary protection from deportation to hundreds of thousands of people who arrived in the United States as children. Trump vowed during the campaign to reverse it.

It was not clear late Tuesday how DACA would be addressed as part of Trump’s immigration actions, if at all, according to a White House official, because of differing views among Trump’s advisers and associates about the timing, scope and political benefits of ending the program or suspending it for new entries.

“Many options are being worked through on DACA,” the official said.

A second person close to Trump noted that Sessions remains highly influential and said during his Senate confirmation hearing this month that ending DACA “would certainly be constitutional.” The person said Sessions and Bannon are working to make sure DACA is addressed but have not finalized a new policy with Trump.

White House aides said Trump planned to meet Wednesday with several parents of children who were killed by immigrants who are in the country illegally. These activists, who refer to themselves as “angel moms,” were frequently featured during Trump’s campaign rallies and during the Republican National Convention.

Any immigration measures announced by the president will set up a fierce battle in Trump’s first week between the White House and advocates for immigrants, who were reacting with alarm Tuesday as word spread that immigration was on the table. Immigration experts said they had been told the orders later this week would include a halt to all admissions of refugees for 120 days, including from the Syrian civil war, and a 30-day pause in the issuance of immigrant and non-immigrant visas to people from some predominantly Muslim countries.

DIFFERENCES WITH HOMELAND SECURITY CHIEF

The planned visit to DHS will be Trump’s second to a Cabinet-level agency since he took office Friday. He spoke to employees at the CIA’s headquarters in Northern Virginia on Saturday.

The presidential visit to DHS also would symbolize some of the more controversial parts of Trump’s agenda. He centered his campaign to some degree on his proposal to build a wall along the U.S.-Mexico border to keep out illegal immigrants, a plan that has been vehemently opposed by Democrats and immigrant advocates.

Trump has also promised to beef up immigration enforcement along the border and inside the United States – including a tripling of the number of U.S. Immigration and Customs Enforcement agents – in an expensive and logistically difficult operation to remove millions of people from the country.

Perhaps most in dispute were Trump’s campaign comments on Muslims. He called at one point for a ban on all Muslims entering the United States as a counterterrorism measure and said he would halt immigration from Syria and deport Syrian refugees already in the country.

It is unclear how this week’s executive actions, orchestrated from the White House, will sit with the man who would enforce them: Homeland Security Secretary John F. Kelly. Kelly, a retired Marine general who was confirmed Friday, struck a markedly different tone from the president during his confirmation hearing, saying the controversial southwest border wall might not “be built anytime soon.”

Kelly noted that when he was a Marine officer in Iraq, his forces secured stability in part by reaching out to clerics and other Muslim leaders. He also vowed to promote “tolerance” and said he didn’t think it was appropriate to target any group of people solely based on religion or ethnic background, including through the development of a registry.

DHS declined to comment on Tuesday. But people familiar with the matter said Kelly, known for his blunt manner, is already under intense pressure from the White House to enforce the immigration crackdown on which Trump built his campaign.