When being inducted into a Trotskyist sect you are told about the many "Stalinist betrayals". One of the favorites is the Popular Front in France in the late 1930s where the Communist Party (PCF) formed an antifascist united front with the Socialist Party and the liberal Radical Party. A Popular Front government was formed by the latter two with Communist Party support.
The main problem with the story is that there was no revolution to betray. There was a huge surge in disputes over wages and conditions involving the occupation of thousands of workplaces. There was also considerable growth in the revolutionary movement and communist party membership mushroomed. However, what you cannot say is that there was a revolutionary situation. The bourgeoisie was way too strong and the working class still very wet behind the ears.
Talk of revolution in these conditions was foolish if not dangerous. But this did not stop the small Trot group in France from calling for workers militias and factory committees to organize an uprising.
And regardless of one's assessment of the internal balance of forces, there were the Nazis on the other side of the border. Any convulsion that significantly weakened France's military capacity would have been an open invitation to invade, and any revolutionary forces would have been crushed by the German steamroller.
It may well be that the Communist Party (PCF) could have been more effective in ensuring that workers were better organized and legally protected when the inevitable employer counter-attack struck. But in the scale of betrayals it scarcely registers.
In all this the PCF is criticized for being a compliant local branch of Moscow's Comintern. I think the latter's policy of collective security against the aggressor fascist powers was a correct one. Endeavoring to ensure a bourgeois government that supported such a policy was perfectly fine. Of course, for the Trots any idea of siding with one imperialist power against another was anathema. Indeed, when war broke out Trotsky believed an Allied victory would be just as fascist as an Axis one.
The Comintern connection did, however, become a problem with the German-Soviet Neutrality Pact that was signed a week before the outbreak of World War II. As discussed in an earlier post, the pact was necessary to ensure that the Soviet Union was not stuck fighting the Germans on its own. However, there was no reason for anybody to be indifferent to the outcome of France's war with Germany. Quite the opposite. The PCF did not handle this very well.
Marxists do need to assess material conditions before making political decisions. Whilst capitalism organises around the nation state, it is reasonable for communists to so as well not withstanding the international solidarity of communist workers. Whilst the comintern over reached in many instances, its political errors were made in difficult circumstances. Hindsight is always 20 20.