PARIS — President Nicolas Sarkozy is an unusually solid French friend of America. He is also a “mercurial” man operating in “a zone of monarch-like impunity” surrounded by advisers often too fearful to give honest counsel, according to leaked cables from the United States Embassy in Paris.

Last December, the American ambassador shared an anecdote with Secretary of State Hillary Rodham Clinton: when the mayor of Paris had the Eiffel Tower lighted in Turkey’s national colors for a visit by Prime Minister Recep Tayyip Erdogan in April 2009, aides to Mr. Sarkozy, a staunch opponent of Turkey’s entry to the European Union, rerouted the presidential plane so he would not see it.

“Élysée contacts have reported to us the great lengths they will go to avoid disagreeing” with Mr. Sarkozy “or provoking his displeasure,” said the cable, signed by Ambassador Charles H. Rivkin. It was part of a trove of documents obtained by WikiLeaks and made available to several news organizations.

Five years of correspondence between Paris and Washington chronicle a spectacular post-Iraq turnabout between one of the West’s most complicated diplomatic couples. Mr. Sarkozy, who took office in May 2007, was described even last year as “the most pro-American French president since World War II” and a “force multiplier” for American foreign policy interests.