The DSA has shown that they can win some blue districts, but they haven’t shown that they can win elections that, without their supposed DSA advantages, would have been won by a Republican.
The socialist politician to have won the most support on a national level is Bernie Sanders, and he is not a member of the DSA.
Republicans love running against the DSA and right-wing media likes plastering Democrats as the DSA, but Democrats are not the DSA. We are talking about a handful of successful politicians, not most Democrats.