Candidate Trump, meet President Trump

On the day Donald Trump launched his presidential campaign, he made dealing with Mexico the keystone of his speech. From then on, he continually advocated keeping Mexicans out of the U.S. and American jobs out of Mexico.

Candidates promise what voters want to hear, although they may well know that keeping their promises will be impossible. That makes them look like liars, inevitably disappointing some of their supporters.

President Trump is about to discover that the most he can do with any certainty is build a wall and even that won't produce the desired result. He cannot make good on the central promises on which he launched his campaign.

Some of Trump's backers feared the country is being swamped by Latino immigrants. They were enthusiastic about his proposal to build a wall, paid for by Mexico, as a way of stopping the flow. He also promised massive deportations of Mexicans.

Not that it matters. It's too late. Even if another Latino never enters the country, there are now more than 56.6 million Hispanics here – 17.6% of the population, growing at a faster rate than the population as a whole. The goal of the wall in keeping down their their numbers cannot be achieved.

What about deportation? Obama oversaw the removal of 2.5 million illegal immigrants, the record for any president. G.W. Bush had previously expelled more than 2 million. Many deported were not even Mexican, who are only a part of the pool of undocumented immigrants.

Continuing Bush-Obama policies can't change the overall demographics much. And nobody can simply be tossed out. Everybody, including illegal aliens, are entitled to due process of law.

He may get the wall built, but Mexico won't write a check to pay for it. Trump knows that and is thinking of a tax. One possibility is a levy on funds transferred to Mexico, targeting remittances by immigrants, legal or not.

A tax on funds leaving the country for Mexico would have to apply to everyone, not only undocumented Mexicans. That would amount to a tax increase on anybody doing business with Mexico. Opposition to a higher tax could leave the U.S. with a wall that it has paid for.

Of course, few people favor unlimited illegal immigration. To really limit it, more border patrol guards could be more effective than a wall, also cheaper and faster. But that's not what was promised.

What about more protectionism by ending the North American Free Trade Agreement, setting higher tariffs on imports from Mexico and discouraging job growth by pressing American firms not to invest there? The goal: keep jobs in the U.S. and bring some home.

More jobs in Mexico cut down on the incentive for Mexicans to move to the U.S. looking for work. And a prosperous economy there helps provide a more solid and stable neighbor.

Protectionism is the hallmark of weakness. Can America no longer compete in the world? Trump promises to “make America great again,” but boosting tariffs could make the U.S. look weak, leading to a loss of respect and influence. It's already happening.

Increasing U.S. protection against imports from Mexico without any legitimate reason would allow Mexico to raise its own tariffs on imports from the U.S. That would cost American jobs, just the opposite of what Trump intends.

Without lower cost imports, prices will increase in the U.S. In effect, a policy to increase American jobs by displacing lower cost imports would amount to saying American consumers have agreed to pay the added cost of keeping jobs here. Is that what voters wanted last November?

Suppose an American automobile manufacturer closes a plant there and shifts production to the U.S. Mexico might use the abandoned plant to produce cars for Mexicans and the rest of Latin America, costing the American manufacturer a market.

Meanwhile, technology, a major cause of lost manufacturing jobs, will be a factor in the car production brought back home. The car company will automate, trying to keep labor costs down.

Because of Trump's inevitable inability to keep his campaign promises on dealing with Mexico, some of his supporters are sure to be disappointed, even disaffected. That, too, is inevitable, and it could happen again and again.

Instead of confrontation with Mexico that sounds better than it is, and is sure to fail, how about “The Art of the Deal,” in which Trump claims to excel?

Otherwise, the passage from Trump Tower to Trump power may prove to be a great disappointment to many of the people who put him in office.