LAST WEEK’S Wall Street Journal/NBC News poll shows that voters think Donald Trump would handle the economy better than would Hillary Clinton. But from his destructive tax proposals to the illogical energy plan he detailed on Thursday, there is little basis for that belief.

Mr. Trump’s vision on energy, as on almost everything, starts with the premise that the country’s politicians have sold out the American people. President Obama has “done everything he can to keep us dependent on others,” he argued, with a policy of “death by a thousand cuts through an onslaught of regulations” on oil, gas and coal. Mr. Trump’s headline policy is “complete American energy independence” by “lifting these draconian barriers” so that “we are no longer at the mercy of global markets.”

Setting “energy independence” as an overriding policy goal is a policy mistake of long standing in Washington. In fact it is far less risky to participate in the global market than to erect barriers to energy imports or ban them entirely. If you rely only on yourself for your oil, you put all of your eggs in one supply basket. Disruptions due to a natural disaster or anything else that would be relatively localized in a global oil market would cause major volatility in a closed domestic one. The best way to insulate the country from oil price volatility would be to make the economy less dependent on oil, but Mr. Trump has no interest in doing so.

Mr. Trump’s error reflects a deeper contradiction in his thinking. He praises the unencumbered free market, insisting that, “the government should not pick winners and losers” and that he would “remove obstacles” in the way of private enterprises. At the same time, he promises energy independence, a renaissance for the coal industry and other goals that would require government interference in the market. The decline of coal, for example, has occurred in large part because under the Obama administration natural gas drilling has boomed, lowering the price of gas and spurring utilities to move away from coal.

Mr. Trump’s plan is dangerous as well as incoherent. In his zeal to revoke environmental regulations, Mr. Trump promises to kill the Environmental Protection Agency’s carbon dioxide rules and pull the country out of the Paris climate agreement. He also promised “clean air and clean water,” but over the past half-century, it has been government regulation, sometimes market-based, that has helped clear up the nation’s air and water. Mr. Trump’s plan would lead to dirtier air and water — and to a massive blow to the global fight against climate change. With great care and difficulty, President Obama persuaded major polluting countries such as China to listen to scientists and move with the United States toward cuts in emissions.

Future generations will suffer if Mr. Trump succeeds in reversing that progress.