Try telling any non-white person "the Democratic party isn't racist." You'll get a big laugh. Unfortunately, racists are everywhere, and more correctly, racism is everywhere. I'm not just talking about klansmen driving around in pickup trucks waving a Confederate flag type of racism. I'm talking about casual racism. It exists in all institutions with hierarchies. Democrat does not equal non-racist. Arguably the party has only done a better job than the Republicans, not a good job on the whole.
Even without the casual racism, there are problematic people in the party. I don't think you should serve in office whatsoever if you have a history of racism. You're not fit to serve the people. The people is comprised of all races. How can someone be a good leader if they don't even have the mental capacity to love all people?