The bill would also lavish benefits on real estate partnerships, hedge funds and other pass-through businesses, which send their profits directly to their owners without taxes being withheld. Republicans want those business owners to pay taxes of just 25 percent on that income, rather than ordinary rates, which go up to 39.6 percent. Republicans argue that this will benefit small businesses. In fact, a large majority of small-business owners already have personal tax rates below 25 percent. This provision would aid a small group of developers, investors and other tycoons who work in professions or industries where it is relatively easy to set up pass-through businesses. Like, yes, Mr. Trump and his family, who make their money from one such industry: real estate. Let’s not forget that Mr. Trump has not released his tax returns, something every other major-party presidential nominee has done for nearly 40 years.

Republican lawmakers argue that they will put in protections to prevent people from turning their salaries into pass-through income. But their promises ring hollow when they are not even bothering to close the carried-interest loophole used by private-equity and hedge-fund managers to treat some of their income as capital gains, which are taxed at a lower rate than wages. Mr. Trump railed against that tax provision during the 2016 campaign.

On personal income taxes, Republicans say they are simplifying and cutting taxes for most people. But that is not really true. They propose reducing the number of tax brackets to four, from seven, while raising the lowest bracket to 12 percent, from 10 percent. They want to double the standard deduction but eliminate personal exemptions. One new benefit that could help many families would be a $300 tax credit for tax filers and their dependents who are over 17, like an aged parent. Strangely, it would end after five years. By contrast, the bill’s cuts to corporate and other business taxes would be permanent.

The changes that could affect middle-class families the hardest include the elimination of the deduction for state and local income taxes. And the property-tax deductible would be capped at $10,000. Many people in high-tax states, like California, New Jersey and New York, would be especially hard hit. Those families would also be squeezed by the proposal to cap the mortgage-interest deduction for home purchases starting Thursday, the day the bill was introduced, at $500,000. Reducing this deduction is worthy of consideration, but it ought to be part of a comprehensive reform of housing subsidies that won’t put home buyers in high-cost areas at a disadvantage.