I DRISS DÉBY , Chad’s president, knows better than most how threatening a Toyota pickup truck can be. In 1990 he seized power after leading 300 of them on a dash through the desert to capture N’Djamena, Chad’s capital. Three years earlier, as army chief, his converted battle-wagons smashed through Libyan lines to end the “Toyota War”. So when three pickup convoys carrying Libya-based rebels were spotted 370 miles into Chadian territory last week Mr Déby had every reason to fret.

Help was at hand. For three days French warplanes strafed the convoys. Chad’s army scooped up the survivors; it claimed to have captured 250 rebels. Chad serves as the headquarters of Operation Barkhane, France’s counter-jihadist mission in five former colonies in the Sahel. In a region that has become fertile territory for Islamists seeking a foothold after the collapse of Islamic State in Syria and Iraq, France sees Mr Déby as a bulwark.

Yet Mr Déby is also a repressive autocrat who has squandered Chad’s oil wealth and beggared his people. He changed the constitution to stay on until 2033 and has won a series of dodgy elections. Emmanuel Macron came to power in 2017 promising to end “Françafrique”, the decades-old policy of propping up African strongmen to serve French interests. He visited Burkina Faso, hoping to atone for France’s role in the escape of Blaise Compaoré, the president toppled in a revolution in 2014. Aiding Mr Déby looks to some like a return to old tricks—though France insists that its forces answered a legitimate request from Mr Déby to foil a coup.

France gave military support to three of Mr Déby’s predecessors. French logistical support also helped Mr Déby beat back rebels who reached N’Djamena in 2008. Yet even when the rebels were shelling the presidential palace itself, France hung back from the direct military intervention seen last week. That the last resort has now become the first response shows how much Mr Macron’s moralising has hit the buffers of African realpolitik.

Not only is Mr Déby viewed as indispensable for Operation Barkhane, but there is little prospect that a replacement would be any better. “The French have never believed that countries like Chad improve and they don’t believe they are susceptible to democratisation,” says Richard Moncrieff of the International Crisis Group, a think-tank. So why risk the downfall of a strongman who serves French interests? Moreover, France can still demonstrate the benefit of its military muscle to African leaders that China, for all its financial might, cannot match.

France’s help should ensure Mr Déby’s survival, for a while at least. Still, France’s intervention is not without its risks. Opposition parties were horrified. Strikes and protests against Mr Déby could yet coalesce into a popular revolt. Should Mr Déby suffer the same fate as Mr Compaoré, a new Chadian leader with genuine popular legitimacy might be inclined to look on France with a jaundiced eye.