WASHINGTON (AP) — When President Donald Trump pulled the plug on an upcoming trip to North Korea by his secretary of state, he pointed a finger of blame at China and the global superpower’s trade practices.

In his recent trade breakthrough with Mexico, Trump praised the country’s outgoing president for his help on border security and agriculture.

Both developments offered fresh evidence of how Trump has made trade policy the connective tissue that ties together different elements of his “America First” foreign policy and syncs up them with his political strategy for the 2020 presidential election.

Trump’s 2016 triumph was paved in part by his support among blue-collar voters in Midwestern manufacturing states that narrowly supported him over Democrat Hillary Clinton, including Michigan, Wisconsin, Ohio and Pennsylvania.

His aggressive trade tactics, epitomized by tariffs and standoffs with longtime economic partners and allies, are aimed at reversing what he has long viewed as unfair trade deals while maintaining support among largely white, working-class voters who have been hurt by the loss of manufacturing jobs.

“Trump understands that economic policy is foreign policy and vice versa,” said Stephen Moore, a former Trump campaign adviser and visiting fellow at The Heritage Foundation. “The most important element of foreign policy is to not just keep the world safe but to also promote America’s economic interest. That’s what Trump does — this is America First.”

It’s also good politics, in Trump’s view.

“It’s a populist position. But it’s also a popular position with a lot of Americans,” Moore said.

As he puts a high premium on trade gains, Trump is intertwining the issue with a host of top foreign policy concerns.

Trump, asked by reporters last week about North Korea living up to its commitments to denuclearize, said “part of the North Korean problem is caused by our trade disputes with China,” pointing to the U.S. trade imbalance with China.

“We have to straighten out our trade relationship because too much money is being lost by us,” Trump said. “And as you know, China is the route to North Korea.”

Trade has been a common refrain at the president’s rallies, where he has vowed to pursue “fair and reciprocal trade.”

“We don’t want stupid trade like we had for so long,” Trump said during a rally in Duluth, Minnesota, in June.

Trump’s second year as president has been marked by a number of trade disputes with traditional U.S. allies and global rivals alike, an approach cemented by his tweet that “trade wars are good.”

He imposed tariffs on steel and aluminum imports in March, prompting retaliation from the European Union and other American allies. Later in the month, Trump announced tariffs on China to combat what he called the theft of U.S. technology from a wide range of goods and services.

China struck back with its own sanctions on a variety of U.S. products, including Midwest farm-produced soybeans in a way to hit hard against the president’s base of voters. The two sides have clashed during the spring and summer, raising the stakes in their trade fight.

In late July, Trump and European Commission President Jean-Claude Juncker reached a temporary deal at the White House to avert tariffs on automobile imports and a ramping up of their trade dispute — although the threat still remains.

After a breakthrough with Mexico, Trump’s team has been engaged in talks with Canada aimed at creating a new version of the 24-year-old North American Free Trade Agreement.

While previous administrations have often used a carrot-and-stick approach to trade as a way to forge agreements, before Trump’s arrival trade agendas had emphasized multi-lateral and bilateral deals aimed at maintaining U.S. leadership around the world, promoting American values and improving human rights.

This administration, by contrast, “is leveraging foreign policy tools to achieve its trade goals,” said Lori Wallach, director of Public Citizen’s Global Trade Watch.

Critics say Trump’s insistence on trade concessions could hamper his ability to move forward in other areas.

On North Korea, for example, Trump has sought to turn his meeting with Kim Jong Un into a vivid example of how his unconventional style can bring longstanding U.S. adversaries to the bargaining table.

But by raising China’s trade practices as essential to any progress to ensuring North Korea gets rid of its nuclear weapons, Trump runs the risk of getting bogged down in both areas — and having little to show for it.

Mixing foreign policy and trade policy introduces so many variables it’s “virtually impossible to close on a precise policy decision,” said Daniel Ujczo, a trade attorney with Dickinson Wright PLLC in Columbus, Ohio. “You’re constantly chasing after the next issue as opposed to having a very targeted approach to the objective.”