The tax breaks for bringing home such offshore profits “confirm the central tenet of tax planning that a tax deferred is a tax avoided,” said David Miller, a tax lawyer at Proskauer Rose. “For decades, U.S. multinationals have shifted profits abroad and deferred their taxes on them. If either of the tax bills pass, they will be rewarded for doing so.”

To be sure, the legislation erects some potential guardrails against future efforts to shift profits offshore. It would establish a minimum tax abroad on certain types of income — at least 10 percent for the first several years in the Senate version — thus raising the tax bills for many companies on their foreign profits. And regulators in Europe and elsewhere abroad have accelerated their efforts to crack down on such profit shifting out of their countries.

President Trump and congressional Republicans argue that it’s important to get companies to bring the money home because it would be used to create jobs — although that didn’t happen the last time lawmakers enacted a similar tax break. Mr. Trump predicted on Tuesday that trillions of dollars would be repatriated — money, he said, that companies currently are “just not able to bring back.”

Under current law, American companies pay taxes on their worldwide profits at a rate of 35 percent, the highest statutory rate in the world. But the law has a big caveat: Companies can indefinitely defer the taxes on profits earned abroad — as long as those profits stay overseas.

That gives companies a powerful incentive to push as much profit as possible into subsidiaries abroad. Microsoft, Merck, Facebook and other companies attribute large chunks of their profits to entities in low- or zero-tax offshore jurisdictions and therefore enjoy effective tax rates that are nowhere near 35 percent.