. How did the labor movement launch a sustained assault on the understanding of freedom grounded in Social Darwinism and the liberty of contract

The correct answer to this open question is the following.

Although there are no options attached we can say the following.

The labor movement launched a sustained assault on the understanding of freedom grounded in Social Darwinism and the liberty of contract in that the labor movement started to question the validity of those affirmations and content.

The labor movement was formed to end the idea that the richest men were the fittest to survive and control poor workers.

The strength of the labor movement relied on the union of the workers to demand better working conditions, the reduction of long hours at the workplace, and the increase of their salaries.

That is the foundation of important labor unions and movements such as the Knights of Labour, the Farmer's Alliance, the IWW, or the AFL.