Why did Biden say to black people: "If you don't vote for me, you're not black"?

Why did Biden say to black people: If you dont vote for me, youre not black?

How does that make any sense? There is a very long list of political parties, and shouldn't all citizens (regardless of their color) be able to freely vote for the party of their choice?

Why did Biden say to black people: "If you don't vote for me, you're not black"?
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