The complicated change could prove crucial to the White House’s revenue plans. Under current law, U.S. multinationals operating abroad must pay an additional tax to the Treasury on foreign profits if they are operating in countries with low tax rates. That tax is avoided by many firms, because they can currently combine their tax rates in high-tax countries with their tax rates in the tax haven. For instance, U.S. companies operating in the Cayman Islands are theoretically supposed to pay the minimum tax. But if they also pay taxes in Germany, a high-tax country, they can effectively zero out that global minimum tax obligation.