For instance, Jackson's The Fall of France states: "[The trial] had become a public relations disaster because Daladier and Blum succeeded in turning the tables on their accusers and demonstrating the flimsiness of the charges against them."
To understand the defense Daladier and Blum putted out during the trial, we can investigate the trial itself, and what it wanted to achieve.
The principal objective of those procedure was to find the responsible for the defeat, the latter being a traumatism for the French population. Therefore, it was in the Vichy’s Government interest to find who was responsible for it. This trial, but the Supreme Court of Justice, and exception jurisdiction created at this occasion, is in line with other procedures targeting the previous government political staff and leaders (for example: de Gaulle trialed and sentences to death by contumacy, other officials arrested). Among Daladier and Blum who both were President of the Council before the war (Prime Minister), the General Gamelin, the Air minister Guy La Chambre and Robert Jacomet, the Army General Inspect, were charged.
Those charged are interesting. The acts creating the Court target “the actions which contributed to pass from the state of peace to the state of war before september 4 1939, and those which later aggravated the situation” (in French: “les actes qui ont concouru au passage de l’état de paix à l’état de guerre avant le 4 septembre 1939, et ceux qui ont ultérieurement aggravé les conséquences de la situation ainsi créée” decree extending the Court competences, 24 september 1940). If at first, following the German’s demands, the instruction looked for responsibilities in the triggering of the war, it was really the “impreparation to war” that was pursued by the instruction.
This trial was publicized quite a lot, and the instruction result was even made available to the public in a printed form. This exposure to the public, enable us to understand why the trial failed.
Wanting to keep the look of a fair trial, in the respect of the rule of law, it started to backfire especially when the lawyers defending Daladier and Blum pointed out the many flaws in the instruction work. Daladier and Blum were good orators, they called on the judges on their principles and those of the French legal system. Those judges who have served in high functions during the IIIrd Republic. They talked about fundamental judiciary principles being violated there, like the non-retroactivity of the penal law, and they highlighted the lack of legal base for such Court. Calling on legal texts such as the Declaration of the Right of Man and the Citizen of 1789. While the Vichy Government wanted to keep the period studied by the Court between 1936 (Leon Blum Popular Front in power) and 1940 (Petain taking over), Blum and Daladier opened this timeline and pointed out numerous instances where the previous government (where Petain was War minister) in the early 30s inactions regarding the German Rearmament. They also pointed out the political aspect of this trial…where they were the only President of the Council from this period charged…the others having rallied Petain weren’t worried. When the accusation tried to put the responsibility of the deficiencies in the war production and army equipment on Leon Blum and the Popular Front (because of the strikes, paid vacations, etc), the defense was about to point out that the previous government (where Petain was in) had done nothing in that regard. Daladier was very precise in the production numbers of various equipment (tanks, anti air, planes, etc). They also pointed out the multiple refusal by Petain to extend the Maginot Line alongside the Belgian border, and the under protection of the Ardennes Forest. They pointed out the refusal by the military high command to change the tactics, which explained why France still fought like WW1, and had no meaningful tank formations and tactics. Also, when he was War Minister in 1934, in a government with full power, Petain accepted a 20% of the army budget. They talked about de Gaulle and the Allied, about their work. Their words are spread by Radio Londres. Seeing that this trial leads nowhere, it is suspended in April 1942, and the Court abolished the next year. Hitler criticized the inability of the judges to declare the French government responsible of the war. Sources (in french)