I can explain that.
In the United States in 1920 or 1930 or thereabouts, racism against black people was basically taken for granted almost like the air you breathe. Even those who disapproved of it usually did not see much hope of a day ever arising when black people could enjoy equality.
In 1964, we had the Voting Rights Act, we had the big Civil Rights movement of the 1960s.
What happened between those times?
World War II. And, after its end, the liberation of Belsen.
The horrors of the Nazi concentration camps changed public attitudes towards racism. Finally, therre was a widespread sentiment that racism was a bad thing.
So this led to progress towards equality for black people.
But now it should also be possible to understand why the failure of Jesse Jackson to immediately and unreservedly condemn Louis Farrakhan's anti-Jewish remarks caused his Presidential bid to sink without a trace.
In an oversimplified picture:
There are two kinds of white American.
The ones who are still happily racist.
Those who have given up racism.
The white Americans in the first category would never have voted for Jesse Jackson.
The white Americans in the second category might consider it - but since the reason they're no longer racist is because they reacted to the Holocaust, their sensitivity towards anti-Jewish racism is many times more intense their sensitivity to anti-black racism. So once Jesse Jackson appeared "soft" on anti-Semitism... goodbye.