Striking a blow at the taxing power of cities and states has long appealed to conservative Republicans. They argue that the deduction works like a subsidy and encourages states — particularly those dominated by Democrats — to set higher rates and spend more taxpayer money.

The deduction is also one of the code’s most costly items. A 2016 report from the Tax Policy Center said ending of the deduction would save the federal government $1.3 trillion over 10 years.

That pot of money is particularly tempting because most of the other big-ticket items in the tax code — including the deduction for mortgage interest and charitable donations — have been labeled off limits by the White House and House Republicans.

The total cost of the president’s tax-related wish list is still a mystery, given the scarcity of detail, but deep cuts in corporate and individual taxes certainly would leave a gaping budget deficit that could run into the trillions.

Like most other deductions, the state and local tax provision primarily benefits wealthier taxpayers who itemize deductions. The Tax Policy Center’s report finds that households with annual incomes exceeding $100,000 would bear roughly 90 percent of the increase; those with incomes over $500,000 would absorb 40 percent. More precise calculations are impossible because other proposals — like eliminating the alternative minimum tax — would create savings for some of these taxpayers.

For example, roughly 30 percent of taxpayers itemize deductions, but that number would certainly fall if the standard deduction were increased, as Mr. Trump proposed, or if various breaks were erased.

While the upper middle class would feel the biggest hit, the wealthiest would mostly be unaffected because of limits on the value of deductions, said Edward D. Kleinbard, a professor of tax law at the University of Southern California. “People affected are those with six-figure incomes, not seven-figure incomes,” he said.