Several hours later, at a campaign rally in Pueblo, Colo., Mr. Trump said that he had used the tax code “brilliantly,” and that his mastery of it meant he was best qualified to overhaul a deeply flawed system.

“I understand the tax laws better than almost anyone, which is why I am the one who can truly fix them,” he said.

Mrs. Clinton wove her attack on Mr. Trump into an address in which she also criticized other corporate actors, including top executives at Wells Fargo after employees opened roughly 1.5 million bank accounts and applied for 565,000 credit cards that may not have been authorized by customers, according to regulators. The bank paid $185 million in fines, including a $100 million penalty from the Consumer Financial Protection Bureau, the largest penalty the agency has ever issued.

Mrs. Clinton seemed upbeat at the rally, her first since the revelations Saturday about Mr. Trump’s taxes. She boasted of being endorsed by LeBron James, who led the Cleveland Cavaliers to the N.B.A. championship and grew up in Akron, Ohio, which Mrs. Clinton was also visiting Monday. “I hope to be elected president, but I know here in Ohio, LeBron will always be the king,” she said.

Mrs. Clinton’s speech fit into a broader economic philosophy, endorsed by her closest economic advisers and often referred to as inclusive capitalism, that calls for corporations to put less emphasis on short-term profits and invest more in employees, the environment and communities.

On Monday, Mrs. Clinton reiterated her proposal to raise the minimum wage, strengthen labor unions and offer tax incentives to companies that share profits with employees. She also unveiled two new policies to protect workers, including curbing the use of “forced arbitration” clauses in contracts that prohibit workers and consumers from bringing legal action against companies that have harmed them.

“We are not going to let corporations like Wells Fargo use these fine-print ‘gotchas’ to escape accountability,” Mrs. Clinton said.