The big problem with Mr. Trump’s tax ideas is that they would leave a multitrillion-dollar deficit for no benefit. Proponents of supply-side economics argue that cutting tax rates encourages people to work and businesses to invest. But the gains are much more modest than proponents claim because many businesses won’t invest unless demand for their products is growing and many people are not motivated by lower tax rates to work more.

On the other hand, significant tax cuts exact very real costs. Mr. Trump’s previous tax plan, released last year, would have reduced federal revenue by $9.5 trillion over 10 years, according to the Tax Policy Center, meaning that Mr. Trump would have to slash government spending or increase borrowing substantially. George W. Bush pushed big tax cuts through Congress in 2001 and 2003 with the promises of strong growth that never materialized.

Mr. Trump also promises to take a machete to existing federal regulations and put a moratorium on new rules. He wants to get rid of environmental policies that he says are driving up the cost of electricity by restricting the production and use of coal and other fossil fuels. In fact, electricity rates, adjusted for inflation, have increased just 2.2 percent, to 12.82 cents per kilowatt-hour, from 2008 to 2015 and are expected to decline to 12.64 cents this year, according to the federal Energy Information Administration.

Increasing fossil fuel production, and the carbon dioxide emissions associated with it, is exactly the wrong strategy at a time when the world has become increasingly concerned about global warming and its disastrous consequences. But this is of little concern to Mr. Trump, who has dismissed climate change as a hoax and whose “energy revolution,” as he outlined it on Monday, made no mention of carbon-free renewable energy sources.

On trade, Mr. Trump renewed his pledge to kill the Trans-Pacific Partnership, an agreement that Mr. Obama negotiated with 11 countries. Mr. Trump claims he can bring back millions of manufacturing jobs to the United States by slapping retaliatory tariffs against China for manipulating its currency, offering illegal subsidies to its exporters and stealing intellectual property from American companies. But such actions would do nothing to recreate jobs that have been replaced by automation, and companies could move production to other developing countries. Mr. Trump’s earlier pledge to put a 45 percent tariff on all Chinese goods would almost certainly start a trade war that would harm American industries that export goods to China.