In 1874, Ulysses S. Grant was president. Levi Strauss received a patent for blue jeans the year before. New York City annexed the Bronx. And the Universal Postal Union was formed, facilitating the exchange of mail across international borders.

That treaty, which turned 145 in July, is now under attack by President Trump, who has threatened to withdraw from it. If he follows through, the consequences could be disruptive for American businesses, which are already getting hammered by new frictions in international exchange created by Trump’s tariffs. But the consequences would also be potentially dire for overseas citizens who would have a harder — and costlier — time casting their ballot in American elections.

You’ve probably never heard of the Universal Postal Union. That’s how it’s supposed to be. It’s an invisible force that allows you to seamlessly receive a letter from Madagascar or a package shipped by a Chinese company.

But those Chinese companies have been getting a bit of a sweetheart deal. Since 1969, China and other poorer countries have been charged lower rates for shipping internationally than richer countries. In effect, those fixed rates have created a system in which Chinese companies can sometimes send parcels that weigh 4.4 pounds or less to the United States for a lower cost than American companies would pay to ship domestically. If that seems unfair to you, you’re not alone.

Trump’s administration has lashed out against the UPU. Last year, the White House formally began the process to withdraw from the treaty. And, for once, Trump has a point: The treaty should be amended to reflect China’s position as an emerging superpower rather than the impoverished backwater it once was. In 1969, China’s GDP per capita was around $100; today it’s nearly $10,000.

The UPU — with representatives from its 192 member states — is holding an Extraordinary Congress this month in Geneva. On the table is an American-led proposal to allow member countries to set their own shipping rates, which would likely see the United States unilaterally increase shipping rates on China. That could spark tit-for-tat retaliation, as with the tariffs. In effect, it would open a new front in the trade war using the postal system — an economic conflict that the UPU was partially designed to prevent. But if the Extraordinary Congress ends without a deal, Trump’s administration has said that the United States will unilaterally withdraw.

As is often the case with Trumpian policy, there would be massive unintended consequences of that withdrawal — and not just for businesses that rely on international shipping. The threat of withdrawal alone is already creating a headache for election officials who are preparing to send out ballots to voters (including soldiers) who are overseas.

In Kentucky, for example, the deadline for sending ballots abroad for state and local elections this November falls before the UPU Congress meets in Geneva. As a result, Kentucky elections director Jared Dearing has voiced concerns that overseas voters will be given incorrect information about how to return their ballots, which, in the best-case scenario, could end up costing voters quite a bit of money to mail their ballots home. In the worst-case scenario, it could lead to thousands of votes left uncounted.

“Military and overseas citizens already face enormous hurdles casting their votes,” Matthew Weil, director of the Bipartisan Policy Center’s Elections Project, told me. “These citizens may be forced to pay up to $70 to return their ballots via private shipping companies, and it’s not clear all states will accept ballots delivered this way.”

In the 2018 midterms, more than 350,000 overseas civilians and military personnel voted from abroad, with the majority using postal ballots, so a significant number of potential voters would be affected.

The economic consequences could also be disastrous, significantly raising the costs of doing business with American companies. That’s why many experts believe that Trump’s threat to withdraw is little more than bluster aimed at securing concessions.

But many experts also believed that Trump wouldn’t follow through on leaving the Paris climate accord or trashing the Iran nuclear deal. As with those blunders, Trump’s approach to the UPU is startlingly slapdash. Rather than courting European allies who also have legitimate beefs with the UPU’s current rates, the White House is yet again going it alone, making the gambit less likely to succeed. And if Trump follows through on his threat to leave the postal union, the U.S. government will have to begin the long slog of bilateral negotiations with the 191 other member states, a massive waste of taxpayer dollars.

In many ways, then, the White House’s latest gamble with the economy is a quintessentially Trumpian move: a bold threat to walk away from a multilateral agreement that works pretty well, while ignoring the unintended consequences that could hurt American business, alienate allies and cause collateral damage to democracy. The best way to put America First is to return to negotiations with a more powerful hand once he’s brought key allies aboard. Otherwise, his dangerous brinkmanship will create more drag on an already flagging economy and could even cost soldiers their right to vote.

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