The indictment accused Mr. Nader of funneling more than $3.5 million in illicit campaign donations through Mr. Khawaja to buy access and influence in Washington — initially with Mrs. Clinton and her Democratic allies during the 2016 campaign, and then with Donald J. Trump after he won the election — to gain “favor” and “potential financial support” from an unnamed foreign government.

A close reading of the 64-page indictment makes clear that the unnamed government is the United Arab Emirates, where Mr. Nader owns a business and advises the crown prince.

At a time of intense debate in Washington over foreign interference in American politics, critics say the scheme outlined in the indictment is one of the most brazen attempts in memory by a foreign power to buy influence during an election. Although lobbyists with foreign clients routinely contribute to campaigns, seldom has a foreign head of state been so personally linked to allegations of evading campaign finance laws.

It is the latest example of an ostensible American ally seeking to shape American policy from the inside, and it is all the more striking because Crown Prince Mohammed, widely known as M.B.Z., is one of the biggest foreign spenders on legal forms of influence — from hiring registered lobbyists to funding think tanks.

“The U.A.E. is emblematic of the foreign influence industry as a whole but they are also exceptionally good at it,” said Ben Freeman, the director of the Foreign Influence Transparency Initiative at the nonpartisan Center for International Policy. “And this is an example of just how far they are willing to go to get the job done: the leader of an alleged U.S. ally who directly violated U.S. campaign finance laws to funnel money to our politicians — that is crazy to me.”