President Trump has long viewed tariffs as a potent weapon for raising revenue, boosting manufacturing and making it easier for American companies to sell their goods abroad.

This week, he deployed the threat of steep duties in more novel fashion by seeking to meddle in another country’s politics, a move that has raised new legal questions about the president’s powers over trade.

On Wednesday, Mr. Trump took aim at Brazil, warning that its exports to the United States could face a 50 percent tariff starting Aug. 1. The high rate was notable, but so was the fact that he linked such a punishing levy to Brazil’s treatment of its former president Jair Bolsonaro.

Mr. Trump sharply attacked the Brazilian authorities for the way they have treated Mr. Bolsonaro, who faces charges that he tried to orchestrate a coup and remain in power after a 2022 election defeat. To Mr. Trump, the allegations amounted to a “Witch Hunt,” and he appeared to demand that Brazil’s courts take action on Mr. Bolsonaro’s behalf; otherwise, the country would face severe trade penalties imminently.

Legal experts described Mr. Trump’s public admonishment as significant, as they questioned whether the president had the authority to issue tariffs in pursuit of purely political objectives. Congress primarily possesses the power to tax imports, though the president may act on his own in limited cases enumerated in law, particularly to protect national security.

Mr. Trump did cite other economic reasons this week for brandishing the steep new duties on Brazil, incorrectly claiming at one point that the United States has a trade deficit with the country. In fact, the United States exports more goods to Brazil than it imports.