That's a good one, but I fear tankies might misuse the immediately following quote for evil:

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.

In 2016, the USA's Green party took enough votes in swing states that had those votes been for the Democrats instead, Clinton would have won.

In December 2018, two reports commissioned by the US Senate found that the Internet Research Agency boosted Stein's candidacy through social media posts, targeting African-American voters in particular.

So, Russia intentionally conned black people into voting for the "workers" party and it lead to a fascist becoming president. Marx might have underestimated the danger on that one.