The trial was held in the city of Riom in central France, and had mainly political aims – namely to project the responsibility of defeat onto the leaders of the left-wing Popular Front government that had been elected 3 May 1936.
The five who stood trial were: More than 400 witnesses were called, many of them soldiers who were supposed to testify that the French army was not adequately equipped to resist the Wehrmacht invasion of May–June 1940.
It was alleged that Blum's legislation, enacted after the 1936 Matignon Agreements which had introduced the 40-hour working week and paid leave for workers and had nationalised some businesses, had undermined France's industrial and defence capabilities.
Owing to the changing international context, including the June 1941 invasion of the USSR, and deterioration of popular support for the Vichy regime, Marshal Philippe Pétain decided to speed up the process.
This was contrary to the principle of nullum crimen, nulla poena sine praevia lege poenali which forbids retroactive application of penal law.
Blum, who was a lawyer as well as a politician and polemicist, turned on what was widely recognised as a brilliant performance, cross-examining the government's witnesses and exposing the falsity and illegitimacy of the charges.
He argued that the largest reductions in defence spending under the Third Republic had taken place under governments in which both Pétain and Pierre Laval, the Vichy regime's prime minister, had held offices.
"[4] Although the court was supposed to investigate only the period from 1936 to 1940, excluding military operations from September 1939 to June 1940, the defendants refused to accept this and demonstrated how the responsibility of the defeat of 1940 rested mainly on failures of the French general staff.
Hitler declared on 15 March 1942: "A trial is taking place these days in France, whose main characteristic is that not a word is spoken about the guilt of those responsible for this war.