By Margaret Talev and Nick Wadhams, Bloomberg News–

President Donald Trump plans to unveil actions on national security starting Wednesday that are expected to include steps toward building a wall on the Mexican border and limiting refugee inflows to the U.S., moving to fulfill key promises he made during his election campaign.

“Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!” the president wrote Tuesday night in a message on his personal Twitter feed.

The announcement on the border wall is expected during a Wednesday afternoon visit by the president to the Department of Homeland Security, the federal agency that has primary jurisdiction over securing the border and would carry out most of the other immigration-related steps that Trump talked about in his run for office.

The Mexican peso reversed early gains to drop to a session low against the U.S. dollar after news of Trump’s plan emerged.

One of the hallmarks of Trump’s presidential run was his pledge to build an impenetrable wall between the U.S. and Mexico to keep out the people “taking our jobs” and to immediately round up and deport “criminal aliens.” He repeatedly said he will make the Mexican government pay for the wall, but may tap existing appropriations for border security at DHS to get construction started. Mexico’s government has rejected the notion that they will ever pay for the wall.

‘Divisive, Polarizing’

“I don’t think Mexico is going to appropriate dollars from their Congress to pay for this,” Representative Michael McCaul, a Texas Republican who chairs the House Homeland Security Committee, said at an event hosted by Bloomberg Government Wednesday morning.

Higher visa fees for citizens of Mexico and Central American countries could help offset the cost, he said. He pegged the price of the wall at $10 billion to $20 billion and said his committee would have to authorize the project.

The border wall — and who will pay for it — is already drawing the ire of Democrats.

“The bottom line here is this is another divisive policy and it’s another polarizing policy,” Senator Ron Wyden of Oregon said in an interview with CNN Wednesday. “I think the American people are going to be able to see through this.”

Trump’s tweet presaged what’s expected to be broader moves in the coming days to curb immigration that would include limits on government programs to settle refugees in the U.S. The Trump administration is considering a 120-day suspension on refugee admissions and a reduction in the number of refugees allowed into the U.S. this fiscal year to 50,000 from 110,000, according to a person familiar with the plan.

During his campaign, Trump warned that the U.S. risked allowing extremists to slip into the country as part of the refugee program, pointing to terrorist attacks such as the killing of a French priest and a bombing at a German music festival, as evidence of the danger posed by refugees. He’s said Germany’s admission of hundreds of thousands of refugees fleeing the Syrian conflict was a “disaster.”

‘Trojan Horse’

Trump once proposed a temporary ban on all Muslim immigration to the U.S.; after drawing bipartisan criticism, he subsequently proposed blocking immigration from countries with a “proven history” of terrorism. Other than Syria, he hadn’t specified what countries would meet that definition during his campaign.

“We’re letting people come in from terrorist nations that shouldn’t be allowed,” Trump said at a campaign rally in September. “This could be the great Trojan horse of all time.”

Under President Barack Obama, the U.S. focused its refugee admissions on individuals with existing links to America, as well as women and children facing persecution or in desperate need of medical care. The screening process averages 12 to 18 months and includes biometric data and reviews by multiple law enforcement and intelligence agencies.