WASHINGTON – With Labor Day now behind us, the final drive for the presidency has begun. But there seems to be a kind of pause in the race as Donald Trump and Hillary Clinton circle each other before their first nationally televised debate at Hofstra University less than three weeks away.

In terms of key policy issues, Trump continues to parade his plan to build a great wall across our southern border and have Mexico pay for it. Clinton, meanwhile, focuses on her wide governmental experience and his total lack of it.

Trump offers little, however, on how that wall will be built, who will build it and how he will make Mexico pay for it. In a terse tweet after a meeting with Trump in Mexico City, President Enrique Pena Nieto flatly rejected the notion that his country would shell out for it.

Trump’s guarantee that the anti-immigration wall will be built comes in the form of his customary “Believe me” assurance. Presumably his oft-touted mastery of “the art of the deal” will somehow turn around the Mexican president.

During the Republican primaries, Trump sent a two-page memo to The Washington Post describing how he would get his way. If elected, he said, he would alter the USA Patriot Act by executive order to deny money transfers known as remittances from Mexicans illegally in the United States to their relatives back home.

The maneuver, he said, would constitute “a one-time payment of $5 to $10 billion” to pay for the wall, which he has estimated elsewhere would cost about $8 billion. Trump suggested that as much as $25 billion goes to Mexico from illegal aliens in the U.S., though the Government Accounting Office has said not all such remittances would be from Mexican immigrants.

President Obama, responding to what he called one of “the wackier questions” about the wall, said that “the notion that we’re going to track every Western Union bit of money that’s being sent to Mexico good luck with that.”

Do many Americans truly believe that such a physical barrier will ever be built, let alone that Mexico will be made to pony up for it?

In a Gallup Poll dated July 20, two-thirds of respondents said they were against building a wall or deporting 11 million undocumented immigrants already here. An overwhelming 84 percent said they favored a path to citizenship for them, an option advocated by Hillary Clinton. Some 38 percent of Republicans said they opposed the wall and 48 percent were against the forced deportations.

Trump in his memo to the Post also mentioned new trade tariffs on Mexican goods and cancellation of visas as further threats to encourage compliance. These steps have not been spelled out in Trump’s numerous massive rallies around the country.

Indeed, the entire Trump campaign pitch is a collection of emotional pleas and promises devoid of details of how he would bring them to fruition as president. This includes his hazy foreign policy agenda marked by hostility toward the NATO allies concerning their financial contributions.

Also very worrisome to many in the American national security establishment is his apparent coziness with Russian President Vladimir Putin, especially in light of reports of Russian hacking into American election cyberspace.

In all, Donald Trump’s presidential campaign is a house of cards, with his wild idea of a border wall as its shaky centerpiece. He now seems to be waffling on certain aspects of his immigration platform, and his new campaign manager, pollster Kellyanne Conway, has promised only that details are “to be determined.” Finding himself under criticism from various quarters, Trump first said there would be “a softening” of his hard line – and then that there wouldn’t.

At the forthcoming first debate, Trump’s house of cards almost certainly will come under structural scrutiny. Both the Trump faithful and the Trump doubtful will be watching and listening, closely, to see how it holds up under greater pressure than that delivered by those adoring rallies chanting “Build the Wall!”