To be sure, the United States has often been willing to mix issues of justice to achieve other ends, such as swapping captured spies with other nations. The Iran nuclear deal offers another example.

As part of the Obama administration’s nuclear agreement with Iran, Iran released five American prisoners and Mr. Obama freed seven Iranian and Iranian-American prisoners. In addition to that swap, the Justice Department also quietly dropped sanctions-related charges and rescinded international arrest warrants against 14 other Iranian fugitives.

But Lisa Monaco, who was Mr. Obama’s top homeland security and counterterrorism adviser during the Iran deal — and the former head of the Justice Department’s national security division — argued that dropping the cases against the 14 Iranians was very different from what Mr. Trump is floating as a possibility in the Huawei case.

For one thing, she said, the Justice Department had concluded it was unlikely ever to be in a position to extradite the Iranians, while American prosecutors are now close to having Ms. Meng in their grasp.

For another, the Iran nuclear deal was an international agreement with numerous other nations, not a common bilateral trade dispute. What is more, it was also a one-time move made in a unique context: a deal to end Iran’s nuclear ambitions without war. Trade negotiations, on the other hand, happen all the time — so the precedent, she said, could endanger Americans.

“I think as a matter of law Trump could direct the Justice Department to drop the prosecution that is the basis of the extradition request,” Ms. Monaco said. “That would be wrong and outside any acceptable norm, and it would be open season on our own executives to be detained and hassled in other countries that want to get leverage in trade talks. But he could do it.”

Curtis Bradley, a Duke University law professor who has written about international law and extradition issues, said what was most unusual about Mr. Trump’s views was that he expressed them publicly as opposed to making them known through diplomatic channels. But he said that from a legal perspective, the decision to request extradition or drop such a request was primarily a matter of foreign affairs, over which the president had broad legal authority.