Nor would Mrs. Clinton’s proposals to increase taxes on people in high-income brackets necessarily have any impact on him, since Mr. Trump apparently wasn’t in an upper bracket for many years. He had no net income to report in the years he paid little or no tax because his near billion-dollar loss in 1995 allowed him to offset income for three previous years and as many as 15 years into the future.

Even so, it wouldn’t be hard to make sure people like Mr. Trump pay at least some federal tax, experts told me this week.

There’s already a simple road map: Although Mr. Trump didn’t have to pay any federal, New York or Connecticut income tax in 1995, he did have to pay income tax in New Jersey. At the time New Jersey took a much tougher approach to the kind of losses Mr. Trump took advantage of than did the federal government. (Under subsequent governors, including Mr. Trump’s staunch ally Chris Christie, New Jersey amended its tax code so it’s now as generous to real estate developers as the federal tax code.)

Since Mr. Trump hasn’t released any of his tax returns, including the schedules from his 1995 returns, it’s impossible to know the precise source of the nearly billion-dollar loss he reported and other losses he used to shelter his income for years. Nonetheless, the returns reveal enough about the loopholes Mr. Trump took advantage of. Here are four simple reforms that would almost surely close them:

Shorten or eliminate the period in which loss carry-overs can be used to offset other income.

Mr. Trump was able to use his enormous loss to shelter income for up to 18 years. Current federal law is even more generous. Businesses and high-net-worth individuals like Mr. Trump, who get most of their income from so-called pass-through entities like partnerships and limited liability companies, can smooth their income streams by using losses to offset income in both past and future years.

Currently, losses realized in one year can be used to offset income reported in the two previous years and can be carried forward for as long as 20 years. The carry-over period was expanded to 20 years from 15 in 1997.