Donald Trump is once again standing in front of America promising a massive new industrial project, billions of dollars in investment and thousands of American jobs.

This time, it is steel.

Trump is promoting a proposed $15 billion steel complex in Iowa that his administration says will eventually become one of the largest steelmaking operations in the United States. The project is being presented as another centerpiece of Trump's promise to bring American manufacturing roaring back.

There is just one problem.

We have heard this before.

In 2017, Trump stood alongside Foxconn executives and Wisconsin officials to announce what was supposed to be one of the greatest manufacturing projects in American history.

Foxconn promised a $10 billion manufacturing complex in Wisconsin. The project was eventually supposed to employ as many as 13,000 people.

Trump didn't merely promote it.

At the project's 2018 groundbreaking, he called it the "eighth wonder of the world."

Then reality arrived.

The enormous factory complex Trump had promoted never materialized as originally envisioned. Wisconsin eventually renegotiated the agreement, dramatically reducing both the required investment and employment targets.

Instead of the promised $10 billion investment and 13,000 jobs, the revised agreement called for approximately $672 million in investment and 1,454 jobs.

Foxconn has continued operating and investing in Wisconsin, so it would be wrong to say that nothing ever came of the project. But the gigantic manufacturing development sold to Americans in 2017 bears little resemblance to what was ultimately built.

Now Trump is making another enormous manufacturing promise.

The proposed Iowa steel project is being promoted with similarly spectacular numbers: approximately $15 billion in investment, thousands of construction jobs, roughly 1,750 permanent jobs and eventually millions of tons of American-made steel every year.

And production isn't expected to begin until around 2030.

In other words, Americans are being asked to celebrate a factory that doesn't yet exist, producing steel that hasn't yet been produced, employing workers who haven't yet been hired, based on investment that hasn't yet been fully made.

Perhaps every piece eventually falls into place.

But Trump's record gives Americans plenty of reason to be skeptical.

Foxconn demonstrates the enormous difference between announcing a multibillion-dollar factory and actually building one.

Trump got the headlines. There was a groundbreaking ceremony. There were speeches, renderings and enormous employment projections.

The "eighth wonder of the world" never arrived.

Now another enormous number is being placed in front of the cameras.

$15 billion.

The lesson from Foxconn isn't that the Iowa project is guaranteed to fail. Nobody can know that yet.

The lesson is much simpler:

Don't judge Trump's manufacturing announcements by the size of the promise.

Come back when the factory is built.