Trump Brags About His Math Skills and Economic Plans. Experts Say Both Are Shaky.

In a combative interview, the former president hinted at even higher tariffs as an economic magic bullet.

Former President Donald J. Trump has been offering up new tax cuts to nearly every group of voters that he meets in recent weeks, shaking the nerves of budget watchers and fiscal hawks who fear his expensive economic promises will explode the nation’s already bulging national debt.

But on Tuesday, Mr. Trump made clear that he was unfazed by such concerns and offered a one-word solution: growth. Despite the doubts of economists from across the political spectrum, Mr. Trump said that he would just juice the economy by the force of his will and scoffed at suggestions that his pledges to abolish taxes on overtime, tips and Social Security benefits could cost as much as $15 trillion.

“I was always very good at mathematics,” Mr. Trump told John Micklethwait, the editor in chief of Bloomberg News, in an interview at the Economic Club of Chicago.

Faced with repeated questioning about how he could possibly grow the economy enough to pay for those tax cuts, Mr. Trump dismissed criticism of his ideas as misguided. He professed his love of tariffs and insisted that surging output would cover the cost of his plans.

“We’re all about growth,” Mr. Trump said, adding that his mix of tax cuts and tariffs would force companies to invest in manufacturing in the United States.

The national debt is approaching $36 trillion. The Committee for a Responsible Federal Budget projected last week that Mr. Trump’s economic agenda could cost as much as $15 trillion over a decade. Economists from the Peterson Institute for International Economics, a nonpartisan think tank, estimated last month that if Mr. Trump’s plans were enacted, the gross domestic product could be 9.7 percent lower than current forecasts, shrinking output and dampening consumer demand.

During his presidency, Mr. Trump repeatedly relied on overly optimistic growth forecasts to make his budget proposals appear to be fiscally responsible. He claimed that his policies would drive more output and generate more investment than they ultimately did. In 2017, he predicted that economic growth would reach 6 percent, but it topped out around 3 percent.

On Tuesday, Mr. Trump maintained that the threat of draconian tariffs would be the centerpiece of his economic agenda. He offered a rationale for imposing across-the-board tariffs of as much as 50 percent — far higher than the 10 percent duties that he previously proposed — and denied the possibility that the tariffs would hurt American businesses.

Instead, at several points during the interview he said such punishing tariffs would encourage companies to set up factories in the United States and would take in revenue for the country.

One idea, the former president said, would be to make the tariff “so high, so horrible, so obnoxious, that they’ll come right away.”

Mr. Trump said the tariff would have to be higher than 10 percent to do that: “They’re not going to do it for 10, but you make a 50 percent tariff, they’re going to come in.”

Mr. Trump imposed tariffs on hundreds of billions of dollars of foreign products during his presidency, but his plans if he is re-elected would dwarf those moves. On previous occasions, Mr. Trump suggested imposing tariffs of 10 to 20 percent on most foreign items, as well as a tariff of 60 percent or more on goods from China, in addition to other levies.

Many economists have said those moves would push up prices for American households and could even threaten to cause a recession in the United States.

When confronted with those criticisms on Tuesday, Mr. Trump disagreed with the idea that tariffs would push up prices for American consumers.

“The most beautiful word in the dictionary is tariff,” Mr. Trump said, adding, “It’s my favorite word.”

During the combative interview, Mr. Trump did not answer whether he would try to remove or demote Jerome H. Powell, the Federal Reserve chair, whom he elevated to the top role at the central bank. He said that while he would not “order” the Fed to raise or lower interest rates, the president should be able to express his views on the matter.

“I think it’s the greatest job in government,” Mr. Trump said. “You show up to the office once a month and you say, ‘Let’s see, flip a coin,’ and everybody talks about you like you’re a god.”

Although economists have projected that Mr. Trump’s economic policies could spur inflation while slowing growth, the former president has maintained — without offering details — that he would simultaneously be able to cut taxes, reduce deficits and keep the U.S. dollar strong.

Asked to explain how his ideas all added up, Mr. Trump praised his math skills and lashed out at Mr. Micklethwait for appearing skeptical.

“You’ve been wrong all your life,” Mr. Trump said.