U.S. presidential candidates Donald Trump and Hillary Clinton have both promised to take steps that would encourage major companies to bring home more of the estimated $2.1 trillion in as-yet-untaxed income they hold offshore.

That amount compares to the roughly $300 billion brought back in 2005 under George W. Bush’s Homeland Investment Act, which slashed the effective tax rate on repatriated funds from 35% to 5.25%.

As this graphic shows, the dollar rose around 10% that year against both the euro and the basket of currencies that measures its broader strength, even if analysts still argue about how far that move was driven by the tax scheme.

Against the yen in the same period it rose 15%.

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“The fact that U.S. corporations hold larger cash piles offshore than ever is a reason why a new repatriation tax holiday could be a bigger boost for the dollar than in 2005,” Morgan Stanley said in a report in July.

“Though we stress the headline number for offshore earnings overstates the unhedged foreign currency amount, which is relevant for FX markets.”

Euro Havens

The U.S. bank also lays out tables of data that it says show where the most money has accumulated. Some 56% of funds have been reinvested in Europe, including 12% and 19% in Ireland and the Netherlands, respectively, compared with 7% each in traditional tax havens like Bermuda and Singapore.

But a trawl through the accounts of the biggest U.S. corporate holders of funds oversees suggests that much of these funds are held in dollars—meaning little or no money would have to be exchanged from, say, euros into dollars.

Apple (AAPL), for example, said last year its $186.9 billion in cash and cash equivalents held by foreign subsidiaries were “generally based in U.S. dollar-denominated holdings.”

As of June 30, 92% of Microsoft’s $113 billion was in U.S. government and agency securities, corporate debt, or mortgage-backed securities.

Given that in 2004 only around $300 billion of an estimated $500 billion in untaxed offshore funds were brought home, that suggests many firms’ repatriations might not involve any foreign exchange at all.

Citigroup chief currency strategist Steven Englander said that even the simple return of dollars to the United States is likely to have a big impact on the currency.

“The dollar money would come back into U.S. equity markets quicker than the non-dollar cash,” he said.

“It would be very good for U.S. equity markets and would probably attract foreign money into the U.S., pushing up U.S. yields in a risk-friendly way. It would be very dollar-positive.”

Englander, who also studied the issue in detail the last time a new repatriation act was being talked up in 2011, says the figure for the amount currently being held abroad is something like $2.5 trillion. Converting even a small share of that huge sum from foreign currencies could be significant.

“No one knows the currency breakdown for sure. Eighty percent in dollars sounds reasonable. So 20 percent of $2.5 trillion is a big number,” he added.