GEOFF BENNETT: President Trump has made repeated claims about the Panama Canal since returning to office, including his contention that China operates it, and he even threatened to take it back.

Economics correspondent Paul Solman looks at some of the history of the canal and the facts surrounding its operation.

PAUL SOLMAN: The Panama Canal, key link between the Pacific and Atlantic Oceans, handling about 5 percent of all global maritime trade, the U.S. its biggest user, it's now a focal target of the president.

DONALD TRUMP, President of the United States: We lost 38,000 people building the Panama Canal.

We have been treated very badly from this foolish gift that should have never been made.

China's running the Panama Canal.

We're going to take it back or something very powerful is going to happen.

PAUL SOLMAN: So, does or doesn't the president have a point?

Well, let's start with a bit of history.

The canal was built by the U.S. from 1904 to 1914.

Why?

So we wouldn't need separate Navy fleets for each ocean.

ANDREW THOMAS, Author, "The Canal of Panama and Globalization: Growth and Challenges in the 21st Century": Which would be a cost savings to the country because they could navigate the canal back and forth Atlantic to Pacific.

And that's why Congress made the investment.

It never really was about trade.

It was about the military.

PAUL SOLMAN: The U.S. spent over 300 million at the time, billions in today's dollars.

And the president says thousands of American lives were lost building the canal.

ANDREW THOMAS: It's estimated probably somewhere on 500 or 600 Americans may have perished.

We know there were thousands and thousands of imported workers from all over the world, particularly Barbados, Jamaica, the West Indies, that did a lot of the heavy lifting, a lot of the day-to-day labor.

Those folks, unfortunately a lot of them died in Panama.

PAUL SOLMAN: The U.S., by treaty, did own the canal, though, and the 10-mile zone next to it.

Why give them away?

ANDREW THOMAS: It was the United States as a self-contained entity there.

It really was a workers' paradise.

People got incredibly well-paid there.

All Americans, those people were getting made three or four times there in the canal zone what they were making in the United States, almost all of it tax-free.

So the Panamanians were locked out.

And it was a sore spot, not just for the United States in terms of foreign policy, certainly for the Panamanians who lived just across the street and saw this incredible world that they really had no ability to access or take advantage of.

We see by 1947 even Harry Truman saying, why don't we get out of Panama gracefully before we get kicked out?

PETER KORNBLUH, National Security Archive: The Panama Canal, people forget, was the leading symbol of U.S. imperial-minded domination of Central America and of the Panamanian people.

PAUL SOLMAN: Which is why President Johnson began the process of negotiating a new treaty.

A decade or so later, Henry Kissinger signed the framework for one.

PETER KORNBLUH: As Henry Kissinger told President Gerald Ford, this is not an issue we want to confront the world on.

It looks like pure colonialism.

PAUL SOLMAN: In 1977, Jimmy Carter finally conceded the canal to Panama.

When Panama took over, it established an independent government authority to run the canal for profit and to modernize it.

And it became a capitalist gem in Central America, not exactly known for such achievements.

RICARDO HAUSMANN, Harvard Kennedy School: The Panamanians after the U.S. returned sovereignty to Panama on the canal, they made a major project, cost them some $6 billion, and it carries ships that can carry a load of three times bigger.

PAUL SOLMAN: Since then, it's become vital to U.S. trade.

JOHN FEELEY, Former U.S.

Ambassador to Panama: If you bought an iPhone or a large screen TV or a washer dryer on the East Coast of the United States in the last decade, you can thank the Panama Canal.

A really important and strategic and overlooked aspect of the canal are liquid natural gas and liquid propane gas exports from the United States that come down the Mississippi River, go out the Gulf of Mexico, or I guess the Gulf of America now, and go through that canal.

There's an entire American industry that depends upon that canal.

PAUL SOLMAN: Made possible by the widened canal lane for, which the authority invested billions of dollars.

It's planning to spend $2 billion more since, in recent years, there's been so much less rain in Panama.

CATIN VASQUEZ, Administrator, Panama Canal Authority: So the Panama Canal is rain-dependent.

So when you have a drought, then we need storage capacity, and that's the reason why we are looking into building a new reservoir, so that we can create a lake to store water to overcome the drought.

PAUL SOLMAN: But the U.S. is by far the canal's biggest customer.

Now that tolls have gone up, shouldn't we get a break?

DONALD TRUMP: American ships are being severely overcharged and not treated fairly in any way, shape or form.

JOHN FEELEY: The tolls have been increased.

They have been increased because of a straight-up capitalist supply-and-demand issue.

There's less water.

There's changing rainfall.

Therefore, they have charged more, but it's very transparent.

You can go on the Web site and find out what the fees are.

PAUL SOLMAN: Maybe the biggest controversy surrounding the canal, though, is China's role.

A Hong Kong-based company, Hutchison, has run two of the canal's five ports since 1997.

ANDREW THOMAS: There was no objection from the United States in any meaningful way to Hutchison, at that time, still a Hong Kong company, soon to be affiliated with China, of course, getting the contract for 25 years to manage the ports on The Atlantic and the Pacific side.

PAUL SOLMAN: Hutchison still operates the two ports, and Chinese companies have since invested billions in Panama.

ANDREW THOMAS: China's playing in our backyard.

I think that's got a lot of people a little concerned.

It's like one day we woke up and all of a sudden Panama and China are very tight.

How did that happen?

PAUL SOLMAN: So, does the Chinese presence pose a threat?

JOHN FEELEY: A port cannot block a canal.

They don't have Chinese warships in the canal.

There are no Chinese soldiers marching up and down the side of the canal.

PAUL SOLMAN: On the other hand, China being there may be a concern for other reasons.

JOHN FEELEY: Chinese commercial expansion, wherever they go in the world, always brings with it issues of corruption, issues of environmental and labor violations, issues of unfair business practices.

PAUL SOLMAN: And, indeed, Panama has announced an audit of Hutchison, whose contract was extended in 2021.

CATIN VASQUEZ: I'm not trying to prejudge whatever the outcome is going to be.

I'm just really looking for a process that is clear, transparent, that, if there is something to be renegotiated, we have the courage, the government has the courage to move forward and proceed accordingly.

ANDREW THOMAS: They will do the re-audit and they will reopen it up for a bit.

And I think you will see an American company be awarded that contract.

PAUL SOLMAN: But does China control the canal?

CATIN VASQUEZ: No, not at all.

This is a Panamanian operation by Constitution.

It's run by Panama.

Only Panamanians are employed here at the Panama Canal.

PAUL SOLMAN: So how are Panamanians reacting?

CATIN VASQUEZ: Most Panamanians feel very strongly that the Panama Canal is Panamanian, that it's being well-managed, it's a transparent, very efficient operation, and it is ours.

RICARDO HAUSMANN: They're feeling whiplash.

I mean, they are the most pro-American country in the region.

They feel that these are just things that are untrue and that they need to clarify because it doesn't reflect reality.

PAUL SOLMAN: They're scared too, right?

RICARDO HAUSMANN: Absolutely scared, because it wouldn't be the first U.S. invasion of Panama.

JOHN FEELEY: If you had to touch the one thing that makes all Panamanians unite around that flag of theirs, it is the Panama Canal.

It is an absolutely essential, existential part of their national being.

PAUL SOLMAN: And threats to the canal, it's argued, could rile up what's long been our strongest non-left-wing ally in the region.

For the "PBS News Hour," Paul Solman.