Emmanuel Macron suffered a serious blow when his Environment Minister resigned, accusing the French Government of falling short on green issues and prey to lobbyists.
Nicolas Hulot, 63, a former TV wildlife presenter seen as the French equivalent of David Attenborough, was one of Macron's most popular ministers.
His appointment was hailed as a coup and he was one of only two in the Cabinet with the title of "minister of state".
However, after a little more than a year in office, he announced his resignation live on national radio, saying that neither the President nor his own wife were aware of his decision.
Hulot, who had voiced reservations from the outset, said he could no longer go on due to an "accumulation of disappointments".
He added: "I don't want to lie to myself any more, or create the illusion that we're facing up to these challenges."
Never a career politician, he said he felt "all alone" on environmental issues in a government committed to a liberal economic model "that is the cause of all the problems".
"We're taking small steps, and France is doing a lot more than other countries, but are little steps enough? The answer is no," he added.
Macron said he respected Hulot's "personal" decision, but his Government had "done more than any other on this subject".
Hulot's appointment bolstered the President's shaky green credentials just 18 months after France brokered the Paris Agreement to fight global greenhouse emissions.
Macron, 40, scored more environmental plaudits for promising to "make our planet great again" after the decision of Donald Trump, the US President, to drop the Paris accord.
But Hulot was clearly frustrated at decisions to water down a string of campaign commitments, notably on cutting the share of nuclear power in French electricity generation from 75 to 50 per cent by 2025.
Macron won power promising EU reform and to reverse chronically high unemployment, but now faces mounting problems.
A senior security aide was filmed assaulting protesters while wearing a borrowed police helmet, and deficit reduction targets have had to be lowered due to slowing growth. Macron's poll ratings are at a record low.
Jean-Luc Mélenchon, the Leftist leader, tweeted after Hulot's departure that "Macronism is starting to decompose."