The Democratic Party is a CAPITALIST party. The inequality, the racism, the support for Big Business, for militarism and war, for imperialism, for ecocide over system change, comes part and parcel out of capitalism. Capitalism and the Democratic Party (and of course the GOP) are inseparable. No genuine progressive (or socialist for that matter) can use an institution for capitalist domination (the Democratic Party) as a vehicle for progressive change. FDR was not a progressive, he prevented the overthrow of US capitalism by making some modest reforms. After US capital was out of danger from real socialists, the US ruling class mounted a witch hunt to purge the labor movement, the left (the main target) of radicals (socialist, communist, anarchist) organizers. We know this today as McCarthyism or more generally as anti-communism. It’s still going on. Since Taft Hartley (under Truman) there has been almost unrelenting attack on the interests of working people. Historically, one of the main roles of the Democratic Party is to divide and confuse the left. They are very good at it. Whatever you think of Sanders, he “sheep dogged” the left into harmless (yes, harmless) electoral politics, which are totally controlled by the duopoly. Look how easy it was for the DNC and HRC to sabotage his campaign. The Democrats are the enemy. Bernie running as a Dem and the DSA supporting him, means the left has been sent to a dead end. It represents a victory for the ruling class, not something to cheer about.