Trump mounts blitz to defend tariff plans ahead of ‘most important case ever’ at Supreme Court

President Trump is sharpening his focus on a Supreme Court fight that could upend his sweeping trade agenda, dubbing it a historic case and terminating Canadian trade talks over alleged interference in the litigation.

Mr. Trump might even cross town to attend oral arguments at the high court on Nov. 5.

“I think it’s one of the most important decisions in the history of the Supreme Court,” Mr. Trump said during a recent Oval Office visit from the NATO secretary-general. “I really believe I have an obligation to go there.”

Blue states and several import-reliant businesses sued Mr. Trump this year, saying he overstepped his powers by invoking the 1997 International Emergency Economic Powers Act to slap reciprocal tariffs on dozens of trading partners and fentanyl-related levies on China, Canada and Mexico.

A ruling against the administration would take a huge bite out of Mr. Trump’s use of tariffs, which are duties on imported goods, and force the U.S. to refund billions of dollars in customs revenue. However, it would not affect sector-specific tariffs imposed on national security grounds, such as those on steel, aluminum, cars and furniture.

Mr. Trump fired off a string of social media posts Friday defending tariffs as vital to national security and the economy. He called the Supreme Court fight the “MOST IMPORTANT CASE EVER.”

More importantly, he canceled trade talks with Canada late Thursday. He said the province of Ontario tried to interfere in the Supreme Court case by running ads that feature President Ronald Reagan’s 1987 warning against the widespread use of tariffs.

“Based on their egregious behavior, ALL TRADE NEGOTIATIONS WITH CANADA ARE HEREBY TERMINATED,” Mr. Trump wrote, adding later: “They only did this to interfere with the decision of the U.S. Supreme Court, and other courts.”

Legal experts say Mr. Trump appears to be building a public relations campaign ahead of arguments before the justices, three of whom are his appointees. And while Mr. Trump’s bare-knuckle tactics aren’t surprising, given his track record and the stakes in the case, a visit to the court would be unusual.

“I think that a president’s attendance at oral arguments would be unorthodox and may well be unprecedented,” said Carl Tobias, a constitutional law professor at the University of Richmond. “The justices are likely to be immune from pressure, and that tactic could backfire if the justices feel pressured to rule for Trump or any specific litigant who appeals a case to the court.”

Clark Packard, a research fellow on trade at the libertarian Cato Institute, said the outcome of the tariff case “is basically a coin flip, and the administration knows that.”

“The tariffs are the centerpiece of the president’s agenda, and a lot hinges on the decision,” Mr. Packard said. “The president attending oral arguments would be highly unusual, but it’s part and parcel with the unusual approach of President Trump more generally.”

Indeed, Mr. Trump is not one to back down from a public fight, and presidents have tried to muscle the Supreme Court throughout American history.

“The list of presidents actively and publicly feuding with or cajoling the Supreme Court is long,” said Thomas Hogan, an associate professor at the South Texas College of Law.

He pointed to President Thomas Jefferson’s complaints about Marbury v. Madison, which established the principle of judicial review. President Franklin D. Roosevelt had a court-packing proposal, and President Barack Obama publicly scolded the assembled court at a State of the Union Address.

“We call it the separation of powers, but it might more aptly be called the ’rules of the brawl,’” Mr. Hogan said.

He said the current court appears to be on board with the idea of a powerful executive branch.

But, he added, “I would think that the president might be concerned that his appearance at a Supreme Court argument could irritate the court members. There are also the pros and cons of the public spectacle.”

The White House did not respond to a request for comment on Friday about whether Mr. Trump is definitely attending the arguments. Mr. Trump will be in Asia this week for major meetings in Malaysia, Japan and South Korea, so the White House may finalize his plans after he returns.

The president is using his Asian tour to negotiate major trade deals with China and South Korea, even as his tariff powers hang in the balance back home.

Mr. Trump secured major deals with Japan, the European Union and the U.K. that may be in jeopardy if the court decides against him, while progress on a new agreement with Canada hit a major speedbump after Ontario ran its ad.

Canada had been negotiating with the U.S. on 35% tariffs on its products. Some goods are exempt under the U.S.-Mexico-Canada agreement that Mr. Trump negotiated in his first term.

Ottawa also wants to reduce high U.S. tariffs on steel, aluminum, cars and car parts.

Prime Minister Mark Carney made a series of concessions to Mr. Trump and had cordial meetings with the U.S. leader at the White House. However, Mr. Trump was enraged by the recent TV ads that use clips of Reagan speaking out against protectionist trade policies.

The clips were taken from a 1987 speech that Reagan delivered during a trade dispute with Japan.

In the remarks, Reagan defended the narrow use of tariffs but said broad-based ones work “only for a short time” and can lead to high prices and retaliation in the long run.

Tariffs are a central plank of Mr. Trump’s economic agenda, so the ads touched a nerve. For months, the president has defended tariffs as a great way to create revenue, gain leverage over other countries and protect U.S. industries.

The Ronald Reagan Presidential Foundation and Institute said Ontario’s ad uses “selective audio and video” to create the ad and “misrepresents” the former president’s remarks, though it did not elaborate.

The ad used different sections of Reagan’s speech together, but does not appear to alter his words.

The foundation said it is exploring its legal options.

In Canada, Mr. Carney said both countries had been making progress in trade talks that could benefit both nations.

“We stand ready to pick up on that progress and build on that progress when the Americans are ready to have those discussions,” Mr. Carney said as he departed Canada for meetings in Asia.

Doug Ford, the premier of Ontario, took out the ad on Oct. 16 because he wanted to make the case against U.S. tariffs by using the words of Reagan, a hero to U.S. conservatives.

The ad cost $75 million Canadian, or $53.3 million U.S., and aired in the U.S. during a playoff baseball game between the Blue Jays and Seattle Mariners.

On Friday, Mr. Ford said he would air the ads during the first two games of the World Series before pulling them on Monday to foster trade talks between the U.S. and Canada.

Mr. Ford’s office, in a statement to CBC Canada, said the ad “uses an unedited excerpt from one of President Reagan’s public addresses, which is available through public domain.”