But Trump's platform faces a major problem: His tax policy could greatly increase the U.S. economy's reliance on foreign goods.

Trump's plan would reduce taxes by between $4.4 trillion and $5.9 trillion over 10 years, before taking into account broader effects on the economy, according to an independent analysis. Trump has said he would cut federal spending to make up for the loss of revenue, but most analysts assume the government would have to borrow more money to make up for the taxes not collected.

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When governments borrow more, their trade deficits -- the difference between imports and exports -- tend to increase. In a brief analysis recently, Len Burman, director of the nonpartisan Tax Policy Center, estimated that Trump's tax plan could double the trade deficit.

Predicting the consequences of Trump's policies is difficult, both because the international economy is immensely complicated and because Trump sometimes has been vague and inconsistent about what he would do if elected. In any case, the fact that Trump's proposal for tax relief could increase the trade deficit illustrates an important connection between the federal budget and global commerce.

Trade and the budget

For decades, Americans have imported more relative to exports when federal borrowing increases. This surprising relationship is reflected in the U.S. "current account balance," an alternative measure of foreign trade that is almost identical to the U.S. trade deficit.

Measured as a share of the size of the overall economy, the current account balance generally has remained within 2 percentage points of the federal budget deficit since at least 1960.

It is not just the United States. One study published by the International Monetary Fund examined the finances of the United States along with 16 other developed nations from 1978 to 2009. The authors found that for every additional dollar a government borrows, the country's current account balance typically increases by 60 cents.

Dollars and debt

The relationship between borrowing and trade comes down to simple supply and demand.

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When the U.S. government borrows more, the Treasury Department sells bonds to raise money at higher interest rates. Borrowers in the private sector, who compete with the government for creditors' money, must accept steeper interest rates as well.

As rates throughout the economy increase, foreign investors buy up dollars to invest them in the United States, where they can earn a good return. There are fewer dollars to go around, and the price of the dollar increases in terms of foreign currencies.

As the dollar increases in price, U.S. firms lose business because their products become more expensive. Exports decline relative to imports, and the trade deficit expands.

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There have been a couple of exceptions to this trend in recent U.S. history. One was at the end of the Clinton administration, when a booming economy not only eliminated the need for federal borrowing but also whetted Americans' appetites for foreign goods. Another exception came during the recent recession, when the economic collapse led to a spike in borrowing and a dip in demand for imports.

Tariffs

In response to critics, Trump has insisted that his proposal would not require the government to borrow more to continue operating, implying a reduction in spending.

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But the New York businessman has not put forward any specific proposals to save the government money. In fact, he has promised to spend more on infrastructure and other costly projects, such as allowing taxpayers to deduct the cost of child care from their income and building a wall along the border with Mexico.

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Indeed, one of Trump's own economic advisers, Tom Barrack, said last week the candidate's policies would cause a substantial increase in federal borrowing.

Trump also has said he would impose steep tariffs on goods from China and Mexico, which supporters might argue would prevent taxpayers from consuming them.

Paradoxically, however, it is not clear whether tariffs would reduce the trade deficit. Americans would exchange fewer of their dollars for foreign currency with which to buy imported goods. As a result, the price of the dollar would increase, again reducing exports, as the nonpartisan Congressional Budget Office explained in a 2000 report on trade policy.

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What's more, foreign countries would likely retaliate with tariffs of their own if Trump carried out his plans. Both exports and imports would decline, and the effect on the trade deficit would be difficult to predict.

From an economist's point of view, a trade deficit is not necessarily detrimental. The deficit can increase because Americans are better off, and it can decline if the country is doing badly.

"Is the trade deficit a good or a bad thing?" asked Kimberly Clausing, an economist at Reed College in Portland, Ore. "There's not a singular answer."