Sometime around the middle of the last century was the peak 'future' for Lefties.
Marxism has always argued that because it was rooted in Engels theory of history that Marxism comprised the entirety of the future. As a consequence, Leftists have always believed that the inevitable future was theirs.
I pick 1959 as the peak year for the Left. The Soviet Union had expanded deep into Europe, re-suppressed Hungary and included Mongolia. China was pure communist. India was an ally of the Soviet Union and marching to the socialist band. Nearly every liberated Third World country was socialist and Latin America was completely in the thrall of Liberation Theology. Castro had conquered Cuba. Nearly all major European businesses were state owned. Canada, Australia, New Zealand were deeply socialist. Roughly 95% of the world was communist or socialist. In the United States labor unions were at their peak.
Need I say more?
From that year forward, the left has been going downhill for 50 years. Today the socialist countries of Europe are facing bankruptcy or have completely changed direction (Sweden, England). Only Cuba and North Korea are still in the thrall of the Left and both are miserable countries. Their citizens are prisoners.
The Left has no future. The future came and went because the idea that humans can be perfected by government action is absurd on the face of it.
Humans change very slowly and only by inducement. Governments have seldom shown the slightest competence in most human organization except in mass murder and popular starvation.