If Congress enacts a similar tax holiday, the prior example suggests that up to $1.7 trillion could be repatriated by U.S. companies. The trouble is, it's unknown how much of the funds are in foreign bank accounts or short-term investments, though estimates suggest that around half of the $2.6 trillion is held in cash. The rest is likely held in other, more illiquid assets like factories and equipment, the note said. Earnings on those resources would be much harder to repatriate.
At a 5.25 percent tax rate, that $1.3 trillion would raise only about $60 billion or $70 billion in tax revenue. Hunter notes that a tax holiday could actually reduce the amount of revenue collected, since companies could take advantage of the lower tax rate on funds they would have repatriated anyway.
A further concern is the suggestion made in the tax plan of shifting to a territorial tax system. That would end the country's taxation of profits from abroad and bring the U.S. closer to other nations, Hunter wrote.
"The upshot is that a tax on reinvested foreign earnings won't come close to paying for the $6 trillion to $7 trillion cost of the massive cuts to individual income and corporate taxes that Trump is proposing," Hunter wrote. "Accordingly, this doesn't change our view that Trump's plan will never make it through Congress in its current form."
The top companies in terms of overseas holdings are Apple, Pfizer and Microsoft, according to a report from the Institute on Taxation and Economic Policy. General Electric and IBM round out the top five.
Watch: Who gains the most from Trump's tax holiday?