Mr. Trump's claim about tariffs lowering taxes amounts to "an argument that says, 'If Americans pay more out of their left pocket, the government will be able to put more in their right pocket,'" said Joe Rosenberg, senior fellow at the Urban-Brookings Tax Policy Center, another think tank focused on taxes.

WASHINGTON—President Trump keeps suggesting that tariffs can replace income taxes for most Americans. One big problem: The math doesn’t work.

President Donald Trump indicated that income taxes will be reduced or even eliminated for many people due to tariffs, with a focus on people earning under $200,000 per year.