President Trump on Friday threatened to close the southern border "entirely" if he does not get the funding he needs for his border wall, saying that it would be a "profit-making operation" to do so. He also said the U.S. would be cutting off "all aid" to three Central American countries -- Honduras, Guatemala and El Salvador -- that he said are the source of immigrant caravans coming to the U.S.

"We build a wall or we close the southern border," he said in a series of Friday morning tweets.

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. Hard to believe there was a Congress & President who would approve! — Donald J. Trump (@realDonaldTrump) December 28, 2018

....The United States looses soooo much money on Trade with Mexico under NAFTA, over 75 Billion Dollars a year (not including Drug Money which would be many times that amount), that I would consider closing the Southern Border a “profit making operation.” We build a Wall or..... — Donald J. Trump (@realDonaldTrump) December 28, 2018

.....close the Southern Border. Bring our car industry back into the United States where it belongs. Go back to pre-NAFTA, before so many of our companies and jobs were so foolishly sent to Mexico. Either we build (finish) the Wall or we close the Border...... — Donald J. Trump (@realDonaldTrump) December 28, 2018

.....Honduras, Guatemala and El Salvador 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. We will be cutting off all aid to these 3 countries - taking advantage of U.S. for years! — Donald J. Trump (@realDonaldTrump) December 28, 2018

Acting Chief of Staff Mick Mulvaney reiterated to reporters that Mr. Trump would be willing to shut down the border, saying "yes" when asked if the president meant what he said in his tweets. CBS has estimated that closing the southern border would cost up to $1 billion a day.

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Still, as the partial government shutdown enters day seven, White House press secretary Sarah Huckabee Sanders told "CBS This Morning" Friday that Mr. Trump is "willing to negotiate" with Democrats on the $5 billion he is requesting to fund the wall.

Sanders blasted Democrats for the standoff that is now expected to keep roughly 800,000 federal workers from receiving paychecks into the New Year, claiming they have "left the table altogether" but not offering details on what the president might be willing to agree to.

"I'm not going to negotiate in the press, but the president has been willing to negotiate on this point and the Democrats have not been willing to do anything," Sanders said. "It's a very sad day when we can't get Democrats to even show up for work and sit down with us and have these conversations and try to help make real solutions and get something done."

Mulvaney also said negotiations have completely shut down, and repeated Sanders' argument that Democrats were more interested in protecting Nancy Pelosi's speakership than the border. Because of this, he said, they did not expect anything substantive until she was elected speaker by Democrat majority on January 3.

Mr. Trump, for his part, plans to stay in Washington in the coming days. Sanders told reporters that "there are no plans as of now" for the president to travel to his resort at Mar-a-Lago. The president had been expected at the Florida resort for New Year's Eve.