.

The only option that polls as beating Trump is Michelle Obama. At least as the Presidential candidate.
As VP, I don't think Michelle Obama would have the same weight in the polls, or even be interested.

I frankly think it's not over yet, and am not certain Kamala Harris will be the candidate.
I think (like Joe Biden in his debate with Trump a month ago) they are similarly setting Kamala Harris up to fail. And when she inevitably has an endless series of gaffes and proves enormously unpopular over the next few weeks, they will leverage her aside in a brokered convention. Where the Democrat-Bolshevik party elites will decide who the presidential nominee will be, and to hell with what 14 million Democrat primary voters who selected Biden think.

The only other that seems logical to me for the Democrats to pick is Hillary Clinton. The prospect of a re-match between her and Trump is just too tempting.
And in Hillary's case, I think she would eagerly take the VP slot, so Frau Hitlery could somehow leverage Kamala aside after the election, to become president herself, at a later date. Perhaps by Kamala's death in a sudden unexpected suicide. rolleyes

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