This is really interesting.
His actions in 1984 were not an endorsement of the KKK. He was (awkwardly) attempting humor through the juxtaposition of a KKK member keeping company with a black person.
To Republicans, he is a cudgel with which to beat Democrats. Criticizing him has nothing to do with really improving race relations. He is a convenient tool to be discarded when no longer useful.
To Democrats, he is a receptacle into which all their hatred of white supremacy can he thrown, and discarded like a used condom.
Do you honestly believe Ralph Northam believes in white supremacy or endorses the KKK? The photo was from 34 years ago he is mocking the KKK. I see no reason to believe he believed in white supremacy and endorsed the KKK even in 1984.
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