Scott Reed, the top political adviser at the U.S. Chamber of Commerce, said on Monday that he had resigned his post, citing what he described as a drift to the political left by the group in the wake of a string of endorsements of Democrats.
Mr. Reed, who was the campaign manager for former Senator Bob Dole when he was the Republican presidential nominee in 1996, also said there was a lack of commitment by the group to spend money to defend the Republican Senate majority ahead of the election on Nov. 3.
In an email, Michelle Russo, a spokeswoman for the group, insisted the chamber had taken action against Mr. Reed “for cause.”
“An internal review has revealed that Reed repeatedly breached confidentiality, distorted facts for his own benefit, withheld information from chamber leadership and leaked internal information to the press,” she said. “We have the documentation of his actions and it is irrefutable. Our decision is not based on a disagreement over political strategy but rather it is the result of Reed’s actions.”
She would not elaborate when asked. Mr. Reed responded that the group’s executive committee should conduct oversight of the organization, and that “a good place to start would be term limits for senior executives.”
Mr. Reed’s departure from the business-minded group, after spending eight years advising it on political decisions, is something of a seismic shift in the Washington establishment.
In recent weeks, the group endorsed nearly two dozen House Democrats, a move that perturbed President Trump and Vice President Mike Pence. Chamber officials said that the endorsements were among a slate that included just over 190 endorsements of Republican House candidates.
David Kochel, a former top adviser to Senator Mitt Romney’s 2012 presidential campaign, said on Twitter that Mr. Reed had “built that place.” Mr. Reed has been described as crucial to ousting former Representative Steve King, Republican of Iowa, who had been criticized as racist for his hard-line views on immigration and who had been a source of discomfort for Washington Republicans for years. The chamber endorsed Mr. King’s G.O.P. primary opponent, Randy Feenstra, who defeated Mr. King in June.
Mr. Reed’s departure comes as Mr. Trump’s own positions on immigration and trade have become sources of discomfort for its member organizations, which generally like free trade and would like to see comprehensive immigration reform.