Washington • With the partial government shutdown headed toward its second week and no resolution in sight, President Donald Trump on Friday issued a string of tweets in which he once again vowed to close the entire U.S. border with Mexico and halt aid to several Latin American countries unless Democrats agree to his demand for billions of dollars in wall funding.

Trump is also canceling plans to visit his Florida resort, Mar-a-Lago, and will remain in Washington over the New Year holiday, Office of Management and Budget Director Mick Mulvaney said.

About 25 percent of the federal government has been shut down since Saturday, with roughly 800,000 workers affected, including an estimated 350,000 who are on furlough at home.

"We will be forced to close the Southern Border entirely if the Obstructionist Democrats do not give us the money to finish the Wall & also change the ridiculous immigration laws that our Country is saddled with," Trump said in a morning tweet.

In a reprise of his threat before the midterm elections to cut off aid to Honduras, Guatemala and El Salvador as a caravan of migrants was making its way toward the United States, Trump said that those three countries "are doing nothing for the United States but taking our money."

“Word is that a new Caravan is forming in Honduras and they are doing nothing about it,” he said, without providing further details. “We will be cutting off all aid to these 3 countries — taking advantage of U.S. for years!”

Despite Trump's threat, the United States this month announced a new collaboration with Mexico on a program to curb migration from Central American countries, with much of the $10.6 billion U.S. contribution to be drawn from existing aid programs.

Trump's tweets come as Congress has effectively given up on breaking the impasse over the president's demands for border-wall funding, all but ensuring that the partial government shutdown will stretch into at least the start of the new year.

The House and the Senate convened for just minutes on Thursday before gaveling closed until next week. During the brief session in the House, Republicans shot down a Democratic attempt to vote on legislation to reopen the government.

As he did Thursday, Trump remained out of public view on Friday. In an appearance on Fox News, Mulvaney said that the president had "canceled his plans for Christmas, and now he's canceled his plan for New Year's."

"He's staying in Washington, D.C., over New Year's," said Mulvaney, who is set to become Trump's acting chief of staff next month.

Even though Trump will be in town and Republicans control both chambers of Congress, Mulvaney acknowledged that little progress on a deal is expected until the start of the new Congress on Jan. 3, when Democrats will retake the House. Contending that Democrats “have simply shut down the discussions,” he sought to place the blame on House Minority Leader Nancy Pelosi, D-Calif., who is expected to be elected speaker in the new Congress.

"Nancy Pelosi, in fairness, does not have the votes for the speakership yet," Mulvaney said. "She cannot be seen by her party as being weak on negotiating with Donald Trump. So we fully expect that until she is elected speaker and has locked that vote up, we don't expect to hear from the Democrats again."

According to a Washington Post tally, Pelosi, who won the Democratic caucus's nomination for the speakership in late November, appears to have secured enough support to be elected speaker in January.

Pelosi's spokesman, Drew Hammill, said in a statement Friday that Democrats "are united against the President's immoral, ineffective and expensive wall — the wall that he specifically promised that Mexico would pay for."

Democrats will not consider any offers that have not been publicly endorsed by Trump himself, he said.

"While we await the president's public proposal, Democrats have made it clear that, under a House Democratic majority, we will vote swiftly to reopen government on Day One," Hammill said.

At the heart of the stalemate is Trump's demand for $5 billion in funding for his proposed wall at the U.S.-Mexico border. Congressional Democrats have rejected that figure and in recent weeks have refused to publicly endorse a figure above $1.3 billion, which continues existing funding levels and includes money for new border fencing and levee walls, but not the concrete wall Trump once demanded before he started more recently talking about "steel slats."

Mulvaney said Friday that "some folks use the term 'wall' and they mean different things."

"Everyone agrees that what we can and should be building on that southern border is that steel barrier that the president tweeted out. That's what he wants to build. The Democrats, believe it or not, don't call that a wall," he said.

The Washington Post’s Erica Werner and Paul Kane contributed to this report.