Leftism these days 
OK, you can make a valid case for social change a la Bernie Sanders: The quality of life in Norway’s (for example) social democratic system is better. That is true and there is, of course, a whole worldwide movement that represents that viewpoint (member parties of the Socialist International).
There is constantly an effort to build such a party or move the Democratic Party in that direction. DSA is on that wave-length.
Social democracy (welfare statism) is better, but its economic system is still essentially capitalist. The paradigm went as far as it could during the twentieth century and then support for it plateaued.
It never fully flourished in this country (came close during the New Deal). I don’t think it ever will. Norway, Sweden, etc. have relatively small and homogeneous populations; small and homogeneous enough as to retain a degree of communitarian sensibility … which is: We take care of each other.
Our country is relatively much larger and much more diverse. Taxation directed to Washington, DC yields very little sense of commonwealth. Social spending occurs by a process that’s opaque, remote, diffuse. Funding the welfare of Others tends to be resented. There are too many nameless Others, far-flung, outside the bounds of “my community.”