President Trump has promised a sweeping tax plan, arriving in the days ahead, that will be “bigger, I believe, than any tax cut ever.” It will aim to bring down individual and corporate rates, simplify the overall tax code and unleash economic growth.

Many tax experts say a key element to any fundamental overhaul is getting rid of certain deductions for businesses — the “special-interest giveaways that are masked as tax breaks,” as House Republicans describe many of them in their own proposal. That is the only way tax rates for much of the country can go down without starving the Treasury, the experts say.

But there is a major roadblock to that fundamental change, and it comes from a sector well known to the president: the real estate industry.

As the nation’s first real estate developer-president — one who has refused to divest his holdings while occupying the Oval Office and has declined to release his past tax returns — Mr. Trump brings his career perspective to the tax question, as well as a substantial financial stake in the outcome.