I have DuBois’s own words saying people in the North didn’t care about black people. Where’s your proof?

You have Dubois saying

they say, I know an excellent colored man in my town; or, I fought at Mechanicsville; or, Do not these Southern outrages make your blood boil?

in reference to how even polite Northerners still saw African-Americans in terms of being an ‘issue’ that needed to be addressed, even if they phrased it positively. He was not seen as a ‘fellow American’, but still othered, even if in an innocently insensitive way.

For those curious, this is a more full quote:

Between me and the other world there is ever an unasked question: unasked by some through feelings of delicacy; by others through the difficulty of rightly framing it. All, nevertheless, flutter round it. They approach me in a half-hesitant sort of way, eye me curiously or compassionately, and then, instead of saying directly, How does it feel to be a problem? they say, I know an excellent colored man in my town; or, I fought at Mechanicsville; or, Do not these Southern outrages make your blood boil? At these I smile, or am interested, or reduce the boiling to a simmer, as the occasion may require. To the real question, How does it feel to be a problem? I answer seldom a word.

So no source for their numbers?

Radical Republicans made up the majority of the Republican majority by 1864 in the Civil War. That would mandate a plurality of voters in at least a quarter of the nation’s electoral districts. Arguably, they made up an outright majority of Congress, which would mandate a plurality of voters in at least half of the nation’s electoral districts.