But the conservative candidate, who was charged Tuesday with misuse of public funds and other offences, is not the only one battling legal woes.
Following is a summary of the cases, great and small, ensnaring the main contenders:
Francois Fillon
The 63-year-old former premier is grappling with the most serious legal problems facing a presidential candidate in modern history following revelations in the French press in late January.
He is accused of misusing public money in respect to payments totalling 680,000 euros ($725,000) to his wife Penelope between 1986 and 2013 from funds made available to lawmakers for parliamentary assistants.
French MPs are allowed to employ family members but Fillon has failed so far to convince investigators that Penelope -- a low-key figure who had previously claimed to have little input into her husband's career -- earned her salary, which exceeded 10,000 euros a month in 2007.
He is also being investigated over payments to two of his children for acting as Senate assistants between 2005 and 2007 as well as payments to Penelope from a literary magazine owned by a billionaire friend of his, Marc Ladreit de Lacharriere.
The staunch Catholic, who had campaigned as a man of integrity, has also been charged for failing to declare a 2013 interest-free loan of 50,000 euros from Ladreit de Lacharriere to a state transparency watchdog.
Fillon has since repaid the loan.
Marine Le Pen
Far-right leader Le Pen, 48, goes into the election with several investigations hanging over her party and her entourage.
One of her close friends and communications advisor, Frederic Chatillon, is accused of illegally funding the National Front's campaign in municipal, European and departmental polls in 2014 and 2015.
Chatillon already faces trial, along with two FN officials, over the party's 2012 general election campaign. The three are accused of setting up a scheme to overcharge for campaign expenses that were reimbursed by the state.
More damaging are allegations that the eurosceptic FN siphoned-off money from Brussels to fund party expenses in France.
The European Parliament accuses the FN of defrauding it to the tune of some 340,000 euros ($360,000) by using funds for parliamentary assistants to pay Le Pen's personal assistant Catherine Griset and her bodyguard Thierry Legier for work back home.
Le Pen has furiously denied any wrongdoing, invoking her immunity as a member of the European Parliament in refusing to attend questioning by investigating magistrates.
Griset has been charged with breach of trust.
Le Pen is also being investigated by French prosecutors for distributing violent images after tweeting pictures of Islamic State atrocities.
Finally, tax authorities are looking into claims that Le Pen and her estranged father, former party leader Jean-Marie Le Pen, failed to declare the full value of family properties. A preliminary investigation has been launched.
Emmanuel Macron
The 39-year-old centrist independent has largely avoided scandal but could be tainted by the fallout from an investigation into possible favouritism over a 2016 event in Las Vegas at which he was the main speaker.
jpegMpeg4-1280x720The glitzy event at the CES electronics fair was organised without a public tender by a unit within the economy ministry, which was then headed by Macron.
Public relations giant Havas was chosen to organise the event, which cost nearly 400,000 euros ($425,000), without bids being sought from other companies.
Macron's team says the investigation targets the event's organisers and not their man, who has been boosted by the scandal engulfing Fillon.
Benoit Hamon
Keen to show that no-one is above reproach, the National Front has drawn attention to a minor affair involving the mild-mannered Socialist candidate, Benoit Hamon.
Hamon, 49, was charged last year with making public insults for calling Nicolas Miguet, a little-known presidential candidate who was fined for conflict of interest in a business deal, a "crook".
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