Investor Carl Icahn, who sold the Trump Taj Mahal casino in Atlantic City after closing it when employees walked out over health insurance and other benefits, is no longer going to advise President Donald Trump on overhauling federal regulations.

During the campaign, Trump suggested Icahn could be treasury secretary. Icahn acquired the bankrupt casino, one of several Atlantic City gambling halls formerly owned by Trump, in 2015, and announced in March that he would sell it to Hard Rock International and two New Jersey investors.

"I sincerely regret that because of your extremely busy schedule, as well as my own, I have not had the opportunity to spend nearly as much time as I'd hoped on regulatory issues," Icahn wrote to Trump.

Government watchdogs said Icahn could personally benefit by changes in regulations, especially concerning ethanol.

"Until a combination of public scrutiny and the lobbying of ethanol interests defeated his effort, Icahn appeared poised to leverage his special status with Trump into a regulatory tweak that would save his refining company $200 million annually," said Robert Weissman, president of Public Citizen, an advocacy group.

"It looked like one of the most extraordinary instances in American history of converting political insider connections into personal profit."

In his letter to Trump, Icahn said there were no conflicts of interest.

"Out of an abundance of caution, the only issues I ever discussed with you were broad matters of policy affecting the refining industry," Icahn said. "I never sought any special benefit for any company with which I have been involved, and have only expressed views that I believed would benefit the refining industry as a whole."