Last month’s pledge by Japan to open its markets to more American cars allowed President Trump to declare victory in a goal he had chased for decades.

For Mr. Trump, the ubiquity of Japanese car brands in the United States is aggravating, when Japan buys virtually no American cars. The disparity has long fed his conviction that the openness of the U.S. economy is not fairly reciprocated, contributing to a persistent trade deficit.

Now, in his second term, Mr. Trump is raising tariffs steeply and pressuring other countries into dismantling barriers that range from taxes on American beef and soybeans to car-safety and local-content requirements in Japan and Indonesia.

Some trade experts question this strategy’s efficacy. They say that countries have in some cases agreed to address specific grievances of Mr. Trump’s, like sales of cars in Japan, that are unlikely to result in a flood of new American exports. Automotive experts and industry veterans who have worked for U.S. carmakers in Japan said the pledge to remove trade barriers might do little to boost sales.

But in the view of supporters of Mr. Trump’s policies, dismantling foreign obstacles to American trade — a longtime goal shared by both Republican and Democratic administrations — is overdue for a more forceful approach.

“Big trade partners have long had rules and regulations in place that lock us out of the market,” said Wilbur Ross, the Secretary of Commerce during the first Trump administration. “The president knows he can go a lot farther than we went last time to rectify those,” he said.

Since World War II, American car companies have never managed to gain a significant foothold in Japan, which hasn’t put tariffs on imported vehicles since the late 1970s. Ford Motor pulled out of Japan in 2016, citing no path to profitability. Last year, American brands like General Motors made up less than 1 percent of sales.

Mr. Trump blames unfair regulations in Japan for making it “impossible” for American companies to sell cars in the market. These include Japan’s unwillingness to accept vehicles that pass U.S. safety standards, which are different than international ones. Mr. Trump sought to change this in his first term.

Late last month, he succeeded.

In exchange for a 15 percent across-the-board U.S. tariff on its goods — lower than the previously threatened 25 percent — Japan agreed to invest hundreds of billions of dollars in the United States. Mr. Trump was keen on another concession. “Perhaps most importantly,” Mr. Trump wrote in a social media post, “Japan will open their Country to Trade including Cars and Trucks.” That means Japan would allow the import of American-made cars without the unique safety standards and testing it usually requires, the country’s chief trade negotiator said at a recent news conference.

Mr. Trump made a similar declaration last week when announcing a trade deal with South Korea. He said that, in exchange for the same 15 percent tariff rate as Japan, South Korea would begin accepting more American cars and trucks into its market without imposing duties on them. In South Korea, similar to Japan, American brands make up a very small percentage of sales.

In Japan’s case, industry analysts say that safety and testing requirements can add up to tens of thousands of dollars to the cost of American cars imported into the country.

However, some industry experts said they doubt that changes to the standards and testing requirements will boost sales. In Japan, where streets are narrow and often congested, most consumers prefer small, fuel-efficient vehicles, typically with steering wheels on the right. Domestic brands like Toyota, Honda and Nissan offer a wide array of such options.

For American carmakers in Japan, “trade barriers have never been the problem,” said Tsuyoshi Kimura, a professor at Chuo University in Tokyo, who used to work at General Motors from the late 1990s through the early 2000s. Japan is a relatively small and already saturated car market, he said, so most American automakers have not put effort into designing models for the country.

The lineups of American manufacturers are packed with bulky sports-utility vehicles and trucks in part because they struggle to make smaller cars profitably. “Thinking about the basic needs of the market, their cars just don’t fit,” Mr. Kimura said. “Even if it’s been declared that Japan’s opening its car market, it’s unlikely that American cars will sell.”

Mr. Trump’s fixation on American car sales in Japan echoes his past trade negotiation tactics such as his emphasis on U.S. dairy exports during his first-term formulation of the United States-Mexico-Canada Agreement, according to Alan Wolff, a senior fellow at the Peterson Institute for International Economics.

“What could have been negotiated could have been far-reaching, and perhaps more important,” Mr. Wolff said. For example, addressing topics such exchange rates, he said. However, he added, securing agreements to open specific export sectors have “political salience” for Mr. Trump. “They matter to him, and therefore they matter to the United States,” he said.

Mr. Ross, the former commerce secretary, agreed with this sentiment. He spent years as chairman of the Japan Society, a nonprofit dedicated to strengthening U.S.-Japan relations. He said he doubted that regulatory changes would sell customers on American cars.

Still, for Mr. Ross, removing trade barriers in countries like Japan was a matter of principle. He likened the situation to a negotiation he had with a European Union official during Mr. Trump’s first term about the trade bloc’s ban on U.S. chicken sterilized with chlorinated wash.

“I asked, why do you have these trade barriers, and she said ‘Oh, Europeans will never eat those foods,’” Mr. Ross recalled. “I said, well, let’s put them on grocery shelves and clearly mark them and if you’re right, then Europeans won’t eat them, we’ll stop selling them, and we won’t have to argue about it.”

The current Trump administration has continued to pressure the European Union to buy American chickens. As part of its recent trade deal, the European Union agreed to work to address “barriers affecting trade in food and agricultural products,” without detailing further.

For others in Japan, these latest trade negotiations feel somewhat like a rerun of the 1980s and 1990s, when the United States and Japan seemed on the brink of a trade war, in part over the issue of American versus Japanese car sales.

In 1995, Japan agreed to several measures, including encouraging greater dealership access for foreign cars. American sales in Japan ultimately didn’t budge. But Japanese automakers at the time were investing heavily in producing vehicles in the United States and discussions about autos largely faded from U.S.-Japan trade talks.

Around that time, Glen S. Fukushima, then an executive at AT&T and a vice president of the American Chamber of Commerce in Japan, was leaving a meeting with Walter Mondale, the U.S. Ambassador to Japan, when the diplomat noticed that Mr. Fukushima’s company car in Tokyo was a Nissan.

Given the recently concluded agreement aimed at securing more market access for American automakers in Japan, the ambassador suggested to Mr. Fukushima that his driver really should be driving an American car.

Mr. Fukushima took the suggestion and tried out a Cadillac Fleetwood. However, it proved much too large for the turns near his Tokyo residence. He ultimately went back to his Nissan Cima and returned to Mr. Mondale to explain the situation.

“He was a reasonable man,” Mr. Fukushima said. “He understood.”

Hisako Ueno contributed reporting.