Since Friday afternoon, Donald Trump has made three related boasts about his policy toward Mexico. The first is that the president successfully forced our neighbors to impose dramatic new curbs on immigrants, thanks entirely to his tariffs threat. The second is that Mexico “agreed to immediately begin buying large quantities of agricultural product” from American farmers.

And the third is that the bilateral agreement includes secret benefits that Trump isn’t yet prepared to divulge to the public.

It quickly became obvious that the first claim is wrong, because the steps Mexico is taking were agreed to months ago. The second claim was also quickly debunked on a variety of levels, including the fact that there’s nothing in the agreement about agricultural purchases.

As for the Republican’s assurances about secret elements of the agreement, it wasn’t long before Mexican officials conceded they haven’t the foggiest idea what Trump was talking about.

The Mexican foreign minister said Monday that no secret immigration deal existed between his country and the United States, directly contradicting President Trump’s claim on Twitter that a “fully signed and documented” agreement would soon be revealed.

Speaking with reporters, Mexican Foreign Secretary Marcelo Ebrard held up a copy of the signed agreement and pointed to its provisions. Debunking the American president’s odd rhetoric, Ebrard said, “There is no other thing beyond what I have just explained.”

For good measure, the Mexican leader also made clear that Trump’s claim about “buying large quantities of agricultural product” is also untrue.

A reporter asked Trump yesterday why Mexico is denying the existence of a secret deal, if that side deal is real.

“I don’t think they’ll be denying it very long,” he replied.

It’s a curious posture: Trump, whose strained relationship with reality is well documented, insists the secret deal is real, but he can’t tell us what’s in it, when he’ll talk about it, or why the other party in the purported deal seems wholly unaware of it.

Last week, Trump made up a quote from NATO Secretary General Jens Stoltenberg, who soon after made clear that he never said what Trump claimed he said. The incident served as a reminder of a rule the American president occasionally forgets: if he’s going to lie, he should avoid falsehoods that real people can easily discredit.

The Mexico “deal” offers notes in the same key: if Trump is going to make up details about a bilateral agreement, he really ought to avoid inventions that the other country can disprove.