Despite President Trump’s statement that he might intervene in a criminal case against the chief financial officer of Huawei Technologies Co., such a move would break from longstanding tradition and advisers have warned him that his options are limited, according to people familiar with the matter.
When news broke last week of the arrest of Meng Wanzhou, threatening the president’s trade talks with China, he asked for options, according to one person, and advisers told him the arrest and potential prosecution of Ms. Meng was essentially out of his hands.
The arrest was a Justice Department matter, they said, and the White House should stay out of it for now, this person said. There are no immediate plans to intervene in the matter, officials added.
The matter arose when Mr. Trump returned to Washington last week optimistic that his trade talks with Chinese President Xi Jinping had made headway. But stocks didn’t respond as well as he had expected, and on Tuesday Mr. Trump told Reuters he’d be willing to intervene in the case against Ms. Meng if it meant securing a strong agreement.
“If I think it’s good for the country, if I think it’s good for what will be certainly the largest trade deal ever made, which is a very important thing—what’s good for national security—I would certainly intervene if I thought it was necessary,” Mr. Trump said.
“It’s also possible it will be a part of the negotiations,” he added.
After Canadian officials arrested Ms. Meng at the request of the U.S., a judge granted her bail. That has set up a legal skirmish between the U.S. and China, as Washington seeks Ms. Meng’s extradition to face charges stemming from alleged violations of sanctions against Iran.
Canadian officials on Wednesday warned of U.S. political interference in Ms. Meng’s extradition case. “I think it is quite obvious that it ought to be incumbent on parties seeking an extradition from Canada…to ensure that any extradition request is about ensuring that justice is done, is about ensuring that the rule of law is respected, and is not politicized or used for any other purpose,” said Canadian Foreign Minister Chrystia Freeland.
Canada is in a particularly tricky spot. Chinese officials have warned of severe consequences for Canada unless it releases Ms. Meng. On Monday, Chinese authorities detained two Canadians in two different cities on national-security grounds. Canada is seeking information on the charges against the two men.
Mr. Trump last month agreed to suspend the planned increase on Jan. 1 of tariffs on $200 billion in Chinese goods to 25% from 10% in order to give the two countries time to negotiate an agreement. The U.S. also said it would aim to wrap up talks in 90 days, a deadline the Chinese have since accepted.
Many of the areas targeted by China for retaliatory action in the trade dispute are in rural states that supported the president in 2016 and may prove important to his 2020 reelection bid.
Investors have been uncertain that Mr. Trump’s meeting with Mr. Xi in Argentina last month would yield concrete results, and stock prices showed significant volatility last week, a volatility that was exacerbated by the news of Ms. Meng’s arrest.
Former Justice Department officials said that while Mr. Trump’s intervention in the Meng case would be a departure from the norms against White House involvement in criminal cases, there is nothing in the Constitution that bars it. Such actions are more common—though still unusual—if the action is framed as a national-security matter.
While the circumstances were different, President Obama pushed the Justice Department to drop cases against several alleged Iran sanctions violators while negotiating a plan for that country to curb its nuclear program.
“In this trade negotiation, the economic and national-security concerns are increasingly indistinguishable, as is the case with so much of what the U.S. and China are in conflict over at the moment,” said Robert D. Williams, executive director of the Paul Tsai China Center at Yale Law School.
The administration’s concerns about the impact of China’s acquisition of U.S. technology are at the heart of the tensions, he said. If the U.S. becomes less competitive in developing next-generation technologies, Mr. Williams said, it will be harder to maintain its military and intelligence edge.
Earlier this year, Mr. Trump vowed to throw Chinese telecommunication giant
a lifeline after it was cut off from U.S. suppliers. The Commerce Department had directed companies to stop exporting to ZTE in mid-April, saying the Chinese firm violated the terms of a settlement resolving evasion of U.S. sanctions against Iran and North Korea.
Still, by publicly announcing that Ms. Meng’s case could be a bargaining chip, Mr. Trump risked undermining his Justice Department and added “another complicating wrinkle to an already delicate bilateral negotiating process,” Mr. Williams said.
On Capitol Hill Wednesday, Sen. Richard Blumenthal (D., Conn.) pressed top law-enforcement officials on the possible intervention. “Let me ask you whether you think that kind of statement sends a dangerous message to our law-enforcement community,” Mr. Blumenthal said.
John Demers, who heads the Justice Department’s national-security division, said the case against Ms. Meng would proceed if she is extradited from Canada. “What we do at the Justice Department is law enforcement—we don’t do trade,” Mr. Demers said.
The FBI’s top counterintelligence official, Bill Priestap, added, “The New England Patriots have this motto: ‘Do your job.’ I want you to know from the FBI’s end, we are going to continue to do our job.”
—Aruna Viswanatha and Paul Vieira contributed to this article.