Donald Trump spoke before cutting a ribbon during the grand opening of Trump International Hotel on Oct. 26 in Washington, D.C. (Jabin Botsford/The Washington Post)

Can you imagine anyone saying that being president of the United States is only a part-time job? Well, Donald Trump might have an incentive to say just that.

That sounds bizarre. But I think it’s within the realm of possibility for Trump to claim in future years that things such as living in Trump Tower rather than the White House and mentioning his properties at every opportunity are promotional activities. If he can show that he spends more than half his time developing, managing and promoting real estate, it could shelter millions of dollars of his non-real-estate income from federal income tax.

I’m not saying that Trump plans to play this particular tax game. But given that he won’t disclose his tax returns, as presidents and presidential candidates have done for decades — and given how aggressive he’s been about cutting his personal tax bill — it doesn’t seem so far-fetched.

Representatives of Trump’s transition operation and his business operation did not reply to requests for comment. So consider this column informed speculation, based on years covering taxes and Trump.

Why does the question of whether Trump spends more than half his work hours engaging in real estate matter to his tax returns? Because of a 1993 loophole that Congress inserted into the Tax Reform Act of 1986.

The law, actually, tried to close loopholes. Taxpayers were no longer allowed to use tax losses generated by owning rental real estate to offset other income. The idea was to crack down on tax shelters peddled to doctors, lawyers and other high-income types. These shelters produced sizable paper losses, generated by non-cash losses such as depreciation, that investors could use to offset non-real-estate income. The investors didn’t actually lose money.

But real estate developers didn’t like this loophole-closing provision, because it stood to increase their taxes. So developers — including Trump — lobbied Congress to allow active real estate professionals to play by a different set of rules. Congress did that, allowing active real estate players such as Trump to use losses on rental real estate to offset other income, which passive real estate investors were no longer allowed to do.

To be considered an active real estate person, a taxpayer has to spend at least half of his or her work time — a minimum of 750 hours a year — being involved in certain real estate activities.

As I wrote in a column last month, the partial Trump 1995 tax returns made public by the New York Times seem to indicate that Trump used a $15.8 million loss generated by the loophole for active real estate professionals to offset other income. It’s impossible to know for sure, because Trump’s people wouldn’t discuss it. But that’s how his return looked to me.

Is Trump going to try to contend on his tax returns that the presidency is a part-time activity?

“I don’t see why his tax behavior as president will differ from his behavior as a private citizen, given the forgone conclusion that he won’t release his presidential income tax returns,” said Edward Kleinbard, a tax-law professor at the University of Southern California’s Gould School of Law and a former chief of staff of Congress’s Joint Committee on Taxation.

Trump has said repeatedly that there’s nothing to be learned from his tax returns. But I’d argue there’s a lot to be learned. If it turns out that we’ve got a president who has been paying little or nothing in the way of federal income tax for years but isn’t proposing to close any of the loopholes that he personally is using, that would tell us quite a bit.