An influential political power broker who was a witness named in the Mueller report was among eight people charged with conspiring to conceal the source of excessive contributions to groups supporting Hillary Clinton’s 2016 presidential campaign, the Justice Department announced on Tuesday.

Prosecutors say George Nader, a Lebanese-American businessman who was a cooperating witness in Robert Mueller’s investigation into Russian interference in the 2016 presidential election, conspired with Ahmad “Andy” Khawaja, the owner of an online payments company, to conceal more than $3.5 million in donations to the groups. The donations let Mr. Khawaja gain access to Mrs. Clinton during the campaign, and he also visited with President Trump in the Oval Office, according to an investigation by The Associated Press last year.

The indictment, unsealed on Tuesday, does not name Mrs. Clinton as the candidate who received the donations. But the indictment refers to a female candidate, and donor records indicate Mr. Khawaja gave Democrats and a political action committee supporting Mrs. Clinton millions of dollars.

Mr. Nader, who has been a frequent visitor to Mr. Trump’s White House, has spent decades working in international diplomacy. He was an informal adviser to the United Arab Emirates’ crown prince, and he was depicted in the Mueller report as a power broker who would connect people associated with the Trump administration to interests in the Middle East and Russia. Mr. Nader frequently met with administration officials, including Stephen K. Bannon and Jared Kushner, and helped steer some White House policies.