The latest attack on Friday night which left 129 people dead has increased political tensions just weeks ahead of regional elections, and the brief semblance of national unity has quickly frayed.
"How many victims must there be before we use the word (failings)? Were all the implications considered after the January attacks? The answer is no," Sarkozy asked in an interview with Le Monde newspaper.
"Too much time was wasted," said the man hoping to take another run at the presidency in 2017 polls.
He said anti-terrorist measures should have been boosted immediately.
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The January attacks on Charlie Hebdo magazine, police and a Jewish supermarket killed 17 people, and there have been several foiled attacks since.
They have been used as political ammunition by France's right, especially far-right leader Marine Le Pen.
She said Hollande's government "should have resigned" after the attacks.
The security fears, as well as Europe's immigration crisis, are expect to boost the right-wing's takings in the regional polls.
Valls got a standing ovation from his own party when he asked "patriots to come together to combat terrorism."
"It's too late," shouted a lawmaker with Sarkozy's The Republicans party from the benches.
Christian Estrosi, deputy mayor of Nice, was then booed by the left in the rowdy session as he said: "Why must so much blood and tears be shed so that you hear us?"
The government has been forced to defend itself once again after it emerged several of the jihadists had been known to security forces.