Every U.S. presidential election matters to the world. This year’s election matters much more than any previous election – due mainly to a man who is calling for drastic changes to American policies, not least those on security and free trade.

By now, the whole world knows that the “America First” slogan of Donald Trump, the Republican candidate, is a euphemism for neo-isolationism and protectionism. The populist tycoon-turned-politician firmly believes that the U.S. loses more than it gains in its dealings with the outside world.

Specifically, Trump, who was officially anointed as the Republican Party nominee last week, calls for U.S. allies to take larger – he even said 100 percent – shares of the cost of stationing U.S. forces abroad. He also discredits free trade, saying that it only benefits partner countries.

This argument, being made by a man who defied the odds and won the presidential ticket, has huge implications for South Korea. Most of all, the Trump foreign policy line may affect the South Korea-U.S. alliance – which is based on a mutual defense treaty under which the U.S. keeps 28,000 troops here – and the 4-year-old South Korea-U.S. Free Trade Agreement.

Trump had already pinpointed countries like South Korea, Japan and Saudi Arabia as “rich nations” that should shoulder all the expenses for hosting U.S. troops. He is threatening to pull GIs out of those countries and even suggested the possibility of abandoning members of North Atlantic Treaty Organization if they are attacked by Russia.

This neo-isolationist policy will allow more room for countries like China and Russia to become more assertive, which could jeopardize peace and prosperity enjoyed by many countries in the world on the strength of free democracy and market economy.

Regarding South Korea, Trump has been speaking up his determination to force Seoul to pay more for American troops. He did not single out South Korea in his nomination acceptance speech, but had already called South Korea a “free rider.”

“We will completely rebuild our depleted military, and the countries that we protect, at a massive loss, will be asked to pay their fair share,” he said in the acceptance speech.

In a previous interview with the New York Times, Trump said that “there’s no guarantee” that U.S. forces will safeguard peace in Korea. This is a reiteration of his threat to withdraw U.S. forces from South Korea if Seoul – which shoulders half of the cost now -- doesn’t pay more.

Another tenet of Trump’s foreign policy is overhauling free trade, which he argues does America more harm than good. He often mentions the South Korea-U.S. FTA, and in his nomination acceptance speech used it to attack his rival, saying that Hillary Clinton “supported the job-killing trade deal with South Korea.”

Many in the world, as well as in the U.S., still doubt Americans will eventually elect Trump as their leader on Nov. 8, but what is certain is that having been elected as the nominee of a party that has been one of the two pillars of U.S. politics, Trump and what he says should be reckoned with.

It shouldn’t be an exaggeration that Trump has already set changes in South Korea-U.S. relations into motion. One example is Clinton’s indication of a change in her own free trade policy. We need to brace for all possibilities.