President Donald Trump tweeted on Thursday that "MEXICO IS PAYING FOR THE WALL!" on the US southern border.

Trump said Mexico will not send the US any money, but instead his NAFTA-replacement trade deal will pay for the wall in time.

Top Democrats bashed the idea as a waste of money and a disingenuous use of revenues from the deal.

Pelosi previously said funding for Trump's wall is off the table, calling it "immoral, ineffective, expensive."

President Donald Trump tweeted on Thursday that he'd come through on one of his first, biggest, and most outlandish campaign promises by making Mexico pay for the US to construct a wall on its southern border.

According to Trump, Mexico will send no money to the US for the wall's construction. Instead, Trump said his NAFTA-replacement trade deal with Mexico and Canada will somehow pay for it.

"I often stated, 'One way or the other, Mexico is going to pay for the Wall.'" Trump tweeted. "This has never changed. Our new deal with Mexico (and Canada), the USMCA, is so much better than the old, very costly & anti-USA NAFTA deal, that just by the money we save, MEXICO IS PAYING FOR THE WALL!"

Trump's USMCA deal does secure some key gains for the US in its trade relationship with both the Canada and Mexico, but it does not resemble a payment from Mexico to the US.

Trump voiced a similar sentiment in a testy meeting with House Minority Leader Nancy Pelosi and Senate Minority Leader Chuck Schumer. Pelosi pushed back on that idea as a waste and a disingenuous use of revenues from the deal.

Read more: Trump inexplicably told Chuck Schumer and Nancy Pelosi that Mexico would pay for the border wall as part of the landmark new trade deal

President Donald Trump, House Minority Leader Nancy Pelosi, and Vice President Mike Pence in the Oval Office on Tuesday. Mark Wilson/Getty Images

The USMCA includes clauses that aim to shift car manufacturing to the US from Mexico. For example, 40% of each car must be produced by workers making $16 an hour or more to avoid cross-border duties, likely boosting the US and Canada's prospect to host those jobs as their industries can pay higher wages. Also, Mexico agreed to allow imports of certain US cheeses.

Otherwise, the USMCA is very similar to NAFTA. And while Mexican industries may now have to pay some duties to the US, the revenue the US could get likely would take the form of taxes levied on workers and goods sold.

Read more: The US, Canada, and Mexico's newly signed trade pact looks a lot like NAFTA. Here are the key differences between them.

Trump has requested $5 billion in funding for the wall, but Democrats, arguing the wall is unnecessary and ineffective to stop illegal border crossings, want to stick to $1.3 billion for border security funding.

Pelosi previously told Business Insider that funding for Trump's wall is off the table, calling it "immoral, ineffective, expensive."

When announcing his campaign in 2015, Trump insisted the US needed a border wall to keep out illegal immigrants. He accused Mexico of sending undesirable people such as rapists across the border and said the US' southern neighbor would pay for the wall.