President Donald Trump on Wednesday vowed to take “strong action” on securing the U.S.-Mexico border and blasted Democrats for what he contends are the country’s “very weak” immigration laws.

Trump’s latest tweet about the border came less than 24 hours after he said he intends to send U.S. military forces there, something that would be legally tricky. His aides Tuesday evening were forced to issue a statement signaling the administration is moving toward a plan to use the National Guard — not active duty forces — which would be more doable legally.

[Trump’s Idea for Military to Secure Border Is Complicated]

The president again on Wednesday morning called on Congress to “change these Obama era, and other, laws NOW!” And he painted the opposition party as impediment for doing so.

“The Democrats stand in our way,” he wrote, alleging “they want people to pour into our country unchecked….CRIME!”

Watch: Trump’s Tweets Won’t Score a Border Security Deal With Congress

Then he vaguely previewed that his administration “will be taking strong action today.” He did not elaborate.

Our Border Laws are very weak while those of Mexico & Canada are very strong. Congress must change these Obama era, and other, laws NOW! The Democrats stand in our way – they want people to pour into our country unchecked….CRIME! We will be taking strong action today.

— Donald J. Trump (@realDonaldTrump) April 4, 2018

Two White House spokespeople asked for an explanation of what action the president was planning did not immediately respond.

The GOP president’s criticism of Democrats leaves some things out: It comes after Trump helped torpedo a bipartisan immigration bill then rejected an offer that would have given him three years of funding for his border wall program.

But the president is eager to use lawmakers’ inaction on immigration and border security legislation to hammer Democratic incumbents and candidates in November’s midterm elections.

His promise of some kind of action Wednesday came after he raised eyebrows Tuesday with his talk of lining the southern border with military troops.

“Until we can have a wall and proper security, we’re going to be guarding our border with the military,” Trump told reporters during a White House appearance with leaders of Baltic countries. “That’s a big step.”

[WATCH: Trump’s Tweets Won’t Help Score a Border Security Deal with Congress]

National Guard units have been used to support federal law enforcement entities along the border. The 1878 Posse Comitatus Act significantly limits a president’s ability to use active duty military troops to enforce civil laws on U.S. soil. Congress can provide a waiver, but Democrats likely would oppose sending active duty troops to seal the border. The party controls enough seats in the Senate to prevent any waiver legislation from reaching Trump’s desk.

Several White House aides appeared unaware of the posse comitatus law Tuesday afternoon as the West Wing staff tried to respond to Trump’s tough talk. National Security Council staff were seen huddling with communications staffers, all with serious and pained expressions as they moved from closed-door meeting to closed-door meeting.

One White House aide apparently thought a reporter was referring to a song from the popular animated movie “The Lion King.”

“Send me something on that ‘Hakuna Matata’ thing,” he said, heading to another meeting in the frantic hours after another seemingly out-of-the-blue Trump declaration. A reporter did so, firing off an email with a list of policy questions. There was no response.