ADEMONSTRABLY BAD idea in pursuit of a possibly worthy goal is still a bad idea. In this instance, the demonstrably bad idea is giving corporations a federal tax break — make that another tax break — on “repatriated profits,” money they earn overseas and bring home. The goal is an infrastructure bank to help build roads and other projects. Such an entity could help rationalize the hodgepodge of politically dictated projects and leverage private capital. But arithmetic’s basic laws must prevail: You can’t pay for an infrastructure bank with a tax break that costs money.

U.S. firms can now defer paying corporate tax on profits they earn overseas until the money is brought to the United States. The notion of a repatriation tax holiday is that the high U.S. tax rate, 35 percent, deters firms from reinvesting overseas profits and “traps” enormous sums, as much as $1.4 trillion, from being put to productive use in the United States. A temporary tax holiday — a reduced tax rate — would boost revenue in the short term as companies took advantage. But it would cost tens of billions in the longer run from lower taxes on income that would have been brought back eventually. The congressional Joint Committee on Taxation has estimated that cutting the tax rate to 5.25 percent would generate $25.5 billion in the first two years but end up costing $79 billion over 10 years.

Meanwhile, the holiday is not apt to create jobs. A Goldman Sachs analysis concluded that “the short-term economic benefit of such a policy would likely be minimal.” A tax holiday would not produce “a significant change in corporate hiring nor investment plans,” Goldman found, because “most firms with large amounts of overseas profits are likely to have adequate access to financing, so the availability of cash on hand is unlikely to be a constraint on investment.” It would reward companies that maneuvered to shift profits to tax havens. Finally, a tax holiday could have the perverse effect of encouraging companies to shift operations — and jobs — overseas in the expectation of another break down the road.

This is a provably bad idea. Congress passed a repatriation tax holiday in 2004. The Congress­ional Research Service reported “little evidence” that new investment was spurred. A recent study by the Democratic staff of a Senate subcommittee found that the 15 companies that repatriated the most profits, more than $150 billion, ended up cutting their U.S. workforces by nearly 21,000 jobs.

Multinational firms have mounted a furious lobbying campaign for the tax break. They argue that even if companies do not use the money for investment, shareholders who receive higher dividends will boost the economy.

The corporate tax code is a mess of perverse incentives. It should be fixed, not gamed — and in a way that bolsters the country’s bottom line instead of further depleting the national treasury.