“The American Socialist movement was founded on a tradition of political independence from capitalist parties. Besides the heroic example of Eugene Debs, who ran for president five times, and was jailed (by a Democratic President!) for his anti-war activism, there were Congressmen Meyer London and Victor Berger and Mayors like Emil Seidel and Frank Ziedler. Even Bernie Sanders ran successfully as an independent for mayor of Burlington, then Congress and Senate before being bitten by the Democratic Party bug. In 1989 he said 'It is absolutely imperative that the progressive movement raise the issues and the analyses which will educate the people of our nation to begin to understand what the hell is going on. And I honestly don’t believe that that can take place within the Democratic Party.'”
Bernie Sanders has backed the Democratic Party's presidential nominee in every election since he became mayor of Burlington in 1980 without exception. Democratic Socialists of America backed Dukakis in 1988, Kerry in 2004, Obama in 2008, and called for ‘defeating Trump’ in 2016 without formally endorsing Clinton. The tradition of American socialism has changed quite a bit from the days of Eugene Debs.
Furthermore, the aforementioned candidates did not "follow the example set by Karl Marx who argued, in an address to the Central Committee of the Communist League." Marx's 1850 address concerned a very different situation: the victory of a democratic revolution over German absolutism and feudalism in which petty-bourgeois democrats would then become the main opponents and oppressors of the working class. This difference becomes blindingly obvious when you read the full paragraph of Marx's address (which talks about taking ‘terroristic measures’ against counter-revolutionaries) and not just that misleading snippet:
“As soon as the new governments have established themselves, their struggle against the workers will begin. If the workers are to be able to forcibly oppose the democratic petty bourgeois it is essential above all for them to be independently organized and centralized in clubs. At the soonest possible moment after the overthrow of the present governments, the Central Committee will come to Germany and will immediately convene a Congress, submitting to it the necessary proposals for the centralization of the workers’ clubs under a directorate established at the movement’s center of operations. The speedy organization of at least provincial connections between the workers’ clubs is one of the prime requirements for the strengthening and development of the workers’ party; the immediate result of the overthrow of the existing governments will be the election of a national representative body. Here the proletariat must take care: 1) that by sharp practices local authorities and government commissioners do not, under any pretext whatsoever, exclude any section of workers; 2) that workers’ candidates are nominated everywhere in opposition to bourgeois-democratic candidates. As far as possible they should be League members and their election should be pursued by all possible means. Even where there is no prospect of achieving their election the workers must put up their own candidates to preserve their independence, to gauge their own strength and to bring their revolutionary position and party standpoint to public attention. They must not be led astray by the empty phrases of the democrats, who will maintain that the workers’ candidates will split the democratic party and offer the forces of reaction the chance of victory. All such talk means, in the final analysis, that the proletariat is to be swindled. The progress which the proletarian party will make by operating independently in this way is infinitely more important than the disadvantages resulting from the presence of a few reactionaries in the representative body. If the forces of democracy take decisive, terroristic action against the reaction from the very beginning, the reactionary influence in the election will already have been destroyed.”
What is at stake in the 2020 American general election is not a "few reactionaries in the representative body" but control over the world's most powerful executive branch: its military, nuclear arsenal, and U.S. federal agencies like the FBI, ICE, the EPA, the CDC, and so on.
There may be a persuasive socialist case against voting Biden but it does not involve twisting Marx's words or falsifying the history of the socialist movement.