It soon could fall on congressional Republicans to plead with President Donald Trump to rescind Thursday’s pay up-or-else threat to Mexican leaders.

Trump used a morning tweet to respond to Mexican President Enrique Peña Nieto’s rejection of the new U.S. president’s Wednesday directive to begin “immediate” construction of a wall along the countries’ 2,000-mile border.

“If Mexico is unwilling to pay for the badly needed wall, then it would be better to cancel the upcoming meeting,” Trump tweeted from his personal account, referring to next Tuesday’s planned White House meeting with the Mexican leader.

Trump also called the North American Free Trade Agreement a “one-sided” pact that has left the U.S. with a $60 billion trade deficit with its southern neighbor. (The U.S. Trade Representative’s office put America’s goods and services trade deficit at $49.2 billion in 2015.)

The U.S. has a 60 billion dollar trade deficit with Mexico. It has been a one-sided deal from the beginning of NAFTA with massive numbers…

— Donald J. Trump (@realDonaldTrump) January 26, 2017

Peña Nieto on Thursday cancelled the meeting. The night before, he said the very notion of the wall Trump envisions “divides us,” telling ABC News that the 50 Mexican consulates in the U.S. “will convert into authentic advocates for the rights of migrants.”

The back-and-forth was prompted by Trump’s Wednesday signing of an executive order that directs the wall project to begin immediately. The president expressed certitude Wednesday that the Mexican government would pay back Washington for the wall. “I’m just telling you there will be a payment. It will be in a form, perhaps a complicated form. And you have to understand what I’m doing is good for the United States.”

Who’s Going to the Pay For the Wall? Congress!]

Much is at stake. Mexico is America’s third-largest trading partner, with the U.S. sending $236 billion in goods to Mexico. That’s a big reason why  critics are worried that the new president is playing with fire and may complicate a major trading arrangement for the country he now leads.

Though congressional Republican leaders are vowing to fully fund — to what they estimate could be $12 billion to $15 billion, but other experts tag at as much as $25 billion — Trump’s border wall project, some of their members appear more closely aligned with the Mexican president than the American one from their own party.

[Trump’s White House Charm Offensive a Contrast to Solitary Obama]

“The facts have not changed. Building a wall is the most expensive and least effective way to secure the border,” Texas GOP Rep. Will Hurd said. “Each section of the border faces unique geographical, cultural, and technological challenges that would be best addressed with a flexible, sector-by-sector approach that empowers the agents on the ground with the resources they need.”

The two-term Hurd is a former covert CIA officer, and a rising star in the GOP who has won election twice in a district that leans toward the Democrats.

Hurd said his 23rd District includes 800 miles of territory along the U.S.-Mexico border, making him the member of Congress who would represent the largest swath of Trump’s wall. And he has a warning for the 45th chief executive who dubs himself “a builder.”

“It is impossible to build a physical wall in much of its terrain,” Hurd, in a statement, said of his district. “Big Bend National Park and many areas in my district are perfect examples of where a wall is unnecessary and would negatively impact the environment, private property rights, and economy.”

And Sen. John McCain, speaking at the GOP retreat in Philadelphia shortly before the new president arrived to meet with lawmakers, dismissed the effectiveness of a just a physical wall.

Sen. John McCain said that the idea of building a wall along the border with Mexico should not, as a practical matter, be taken literally.

“My general reaction to the ‘wall’ is that border security can be achieved not through just building a wall. Walls can be pierced. Walls can be climbed over. If you ever go to San Diego or even Nogales, Ariz., you’ll see tunnels that we uncover on a weekly basis,” the Arizona Republican said.

Such points sound a lot like those expressed Wednesday by Sen. Patrick J. Leahy of Vermont, the top Democrat on the Senate Appropriations Committee, which would have much of the jurisdiction for funding such a project.

“Our broken immigration system demands a sensible, comprehensive and carefully crafted solution, not expensive political stunts,” Leahy said in a statement. “As a candidate, Donald Trump repeatedly claimed that Mexico would pay for an enormously costly wall.

“Now as President, he plans to have the American taxpayers to pay for it. Billions upon billions of wasted tax dollars,” he said. “A troubling pattern is quickly emerging, with the fuzzy talk about killing the Affordable Care Act, and now with ‘the wall.’ It’s jump first, and make real plans later, if ever. That’s not how we should treat American taxpayers. “This would be a costly and ineffective proxy for real action to fix immigration problems.”

Niels Lesniewski contributed to this story