Near the end of the second presidential debate on Sunday night, the candidates laid out their energy policies in response to an audience member’s question about how they would meet the nation’s energy needs while both minimizing job losses and being environmentally-friendly.

The audience member, Ken Bone, is a coal plant operator in Illinois and became an Internet sensation on Monday.

Republican candidate Donald Trump took the opportunity to predictably attack the Obama administration, saying it has put energy “under siege.” But he also did something more unusual: He touted “clean coal.”

While there are various definitions of clean coal, the most common one refers to the process of capturing and storing the carbon dioxide emitted by coal burning power plants.

Trump said: “We need much more than wind and solar. . . There is a thing called clean coal. Coal will last for a thousand years in this country.” However, the reality of clean coal is that it hasn’t been done economically at a large scale in the U.S., and there’s been a number of clean coal projects that ended in failure.

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Take the most recent, Southern Company’s Kemper clean coal plant in Mississippi that has gone $4 billion over budget and isn’t yet operational. The plant, which has cost close to $7 billion, has taken hundreds of millions of dollars in grants from the federal government. Last week, Southern Company said it was again delaying the project and raised the projected cost.

Then there’s FutureGen, a clean coal project that was in the works for more than a decade. That project, which was intended to be built in Morgan County, Ill, got so expensive that the Bush administration, and then later the Obama administration, cut federal support for it. It never got built.

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NRG Energy says its clean coal Petra Nova project, at the W.A. Parish coal plant near Houston, Tex., is surprisingly on time and on budget. The facility is supposed to be operational by the end of the year.

However, NRG Energy now says the clean coal plant will be its last, because of the drop in oil prices. The company plans to sell the captured carbon dioxide from the plant to oil companies to inject into under performing oil wells as a way to stimulate them to get more oil. But with oil companies hurting, they could be less interested in buying the carbon.

So NRG Energy’s clean coal plant may be completed, but it’s unlikely to set a precedent for profitability.

Meanwhile, China is moving ahead with clean coal like the GreenGen plant, a billion dollar project in the city of Tianjin. But China might have more of an appetite than the U.S. for big spending on clean coal considering the country’s large coal reserves, rapidly growing power needs and hand-wringing over pollution.

As for Trump, he failed to mention that no U.S. major clean coal plant is operational. He also neglected to say that the U.S. coal industry has been struggling partly because of the economics involved. The rise in low cost U.S. natural gas, as well as cheap wind and solar, has done as much to hurt the coal industry as have environmental regulations. When power companies close an aging coal plant, it makes more economic sense for them to build a new natural gas plant, or even solar and wind ones.

Trump continues to say that he’d bring back coal jobs if elected, but it’s unclear how he would do that. Removing regulations—throwing out controversial Obama’s Clean Power Plan that pushes power companies to lower greenhouse gas emissions or rejecting the international Paris Agreement that holds countries to lowering their greenhouse gas emissions—wouldn’t bring the lost jobs back alone.

Neither, likely, will clean coal.