"At its heart, it's a story of missed opportunities," said a government source, speaking on condition of anonymity.
"We knew from the start what would happen in Syria -- the refugees, the attacks -- and we took the right stance, but we lost," he said.
France was perhaps the most adamant in saying that Assad -- whom they labelled a "butcher" of his own people -- was the cause of the civil war in its former colony and had to leave power.
But diplomats admit that strategy was based on an overly optimistic assessment of the changes sweeping the Middle East in 2011 and 2012.
In those early hopeful days of the Arab Spring, France was caught up with the "Egyptian and Tunisian illusion", in the words of one former diplomat, believing that the relatively peaceful revolutions in those countries could last and be replicated in Syria.
"We still thought that Egypt would turn into Switzerland overnight," said the diplomat.
"No one thought Bashar would hold on."
In November 2012, France became the first Western country to recognise the Syrian National Coalition, a coalition of opposition groups, and began discussing the possibility of lifting the European arms embargo so as to provide weapons to "moderate" rebels.
French diplomats shuttled back and forth to Turkey to meet with Syrian rebel leaders, but the conflict was already degenerating into a brutal, multi-front war, complicated by the intervention of regional powers such as Saudi Arabia and Qatar and the rise of Islamic State jihadists.
By the time the European embargo ended in May 2013, France and other Western powers were much less inclined to provide arms to the rebel groups, that were increasingly dominated by extremist jihadists.
"Those who helped the Syrian regime (most notably, Russia and Iran) did so with dedication and stayed the course," said Francois Burgat, head of the French Institute of the Middle East.
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"By contrast, those who wanted to help the opposition have procrastinated and had mood swings. We are all complicit in this great political failure."
LEFT IN THE COLD
Most analysts agree the turning point came on August 31, 2013, when US President Barack Obama refused to strike Assad's regime, even though it had crossed his supposed "red line" by using chemical weapons against civilians, killing at least 1,500 people in a Damascus suburb.
France, which had been poised and eager to strike, suddenly found itself isolated and impotent.
"They let us advance, telling us we were covered. And we found ourselves left naked and out in the cold," a senior counsel at the Elysee Palace told a Le Monde reporter recently.
"Militarily, we didn't have the capacity to go it alone. Diplomatically, we didn't know how to convince the world that we were right," said the government source.
"From that moment on, it was a slow dereliction of duty."
Paris has never fully forgiven the US for that moment, and it has continued to feature in Hollande's assessments of the crisis.
But there was little France could do. By mid-2014, diplomats were talking of a "general sense of hopelessness around the (Syrian) dossier".
"We don't control anything anymore. We've left the job to the actors in the region," a source told AFP at the time.
As the civil war deepened, the Islamic State group expanded and the refugees poured into Europe, France could do little but watch from the sidelines while continuing to call for Assad's departure.
That remains the official line, but priorities are changing in the wake of the deadly IS attacks in Paris.
"What do you do?" said the government source.
"In a context where 130 people have been killed in Paris, where these attacks were fomented in Syria, how do you explain to people that we want a cautious diplomacy?"