I have family that think the same way. "There is no political Left in America."

We have been ruled by Fabian Socialists since the Hoover administration, who started their work at the turn of the 20th century in the Woodrow Wilson administration (someone the Left also thinks is a Rightist, despite being the major force of the "Progressive Era" of American politics). The entirety of progressive positions today were constructed by the most radical communists of the 1970's.

They are standing here telling you that anti-Liberal Communists are "Liberals", and that the people they think would have been cooky fringe, are now mainstream progressive positions.

They look at their current objectives (which were unachievable to every generation before them), and say that since they weren't achieved, they've never had any power, despite nearly all of their predecessor's former objectives having been achieved.

As current_horror points out, for the default Leftists this is mostly ignorance; but for the activists: they are aware of it and using it as a mechanism to push people Leftwards.

In reality, the US became a Democratic Socialist country under FDR and has been very slowly Liberalizing out of Socialism for the past 70 years. Progress has been made on economic grounds, but lost on federal control and social grounds.