Does he have a case?
Many of his supporters and some legal experts say he does, and express suspicions about the unusually aggressive legal tactics used in the case as well as its timing, which could torpedo his possible run for the presidency in 2017.
The string of accusations against Mr. Sarkozy — garnered in part from secretly recorded conversations of the former president and his lawyer — include that he sought confidential information from an influential judge and financed his 2007 presidential campaign with $68 million in illegal funds from Col. Muammar el-Qaddafi of Libya. If charged and found guilty of the most serious charge, he could face up to 10 years behind bars.
The Socialist prime minister, Manuel Valls, has insisted that the government is not behind the case. But critics, not least of them Mr. Sarkozy, say that such claims ring hollow in a country where the internecine battles between right and left are virulent.
Read MoreSarkozy's legal woes: Au revoir presidential hopes?
Mr. Sarkozy's supporters argue that the timing of the case against Mr. Sarkozy is no coincidence. President François Hollande, a Socialist and longtime political foe of Mr. Sarkozy's, is buffeted by record-low approval ratings, a sluggish economy and infighting among his party ranks. Sébastien Huyghe, a parliamentarian and member of Mr. Sarkozy's rightist Union for a Popular Movement party, argued that Mr. Sarkozy's misfortunes were calculated to revive Mr. Hollande's own sagging political prospects.
"I think that people on the left are significantly concerned by Mr. Sarkozy's political comeback," he said. "They've named judges who don't like Sarkozy, and it is very insidious. I am convinced that the president of the republic is deeply afraid of Mr. Sarkozy. His greatest fear is to run against him in 2017, and he will use any means possible to beat him."
While there is no evidence of Mr. Hollande's direct involvement in the case, some see a personal vendetta at work. The bitter rivalry between Mr. Sarkozy and Mr. Hollande has sometimes boiled over into barely concealed hatred. During the 2012 presidential campaign, Mr. Sarkozy calleMr. Hollande "useless" and a liar, and said he had not achieved anything in 30 years of politics. Mr. Hollande, in turn, described Mr. Sarkozy as a "salopard," or bastard.
The political timing of the case also raises questions, coming at a decidedly bad time for Mr. Sarkozy's party, battered by a leadership crisis and adrift politically. Before the latest scandal, Mr. Sarkozy was viewed as a likely candidate to lead the party, which will choose a leader in November. Now that he is tainted, his prospects are significantly diminished.
Read MoreFrench court puts Sarkozy under formal probe
Though evidence of a conspiracy is circumstantial at best, few disagree that Mr. Sarkozy is despised on the left. Both as a former interior minister, and then as president, he deeply infuriated the left by advocating free markets, espousing a zero-tolerance approach to crime and characterizing the judiciary as an insipid clique too soft on criminals.
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Some political observers have suggested that his contempt for the judiciary is coming back to haunt him. Mr. Sarkozy sought last week to cast doubts on one of the judges on the case, Claire Thépaut, noting that she was a member of a leftist magistrate's union. Others have observed that the newly established anticorruption prosecutor's office pursuing the case against Mr. Sarkozy was established under a Socialist government in January.
Jean-Jérôme Bertolus, a leading commentator for the French broadcaster Itele, noted that in the Sarkozy camp, Ms. Thépaut was considered "a personal enemy." Asked about Mr. Sarkozy's election defeat in 2012 by a journalist for Mediapart, a news website, Ms. Thépaut replied, "What is certain is that we hope to return to calm, serenity and confidence."