There is a huge difference between the liberal/conservative vs. Republican/Democrat argument. Only those who see in black in white would argue that only Republicans or Democrats have helped/hinder blacks.
William McCulloch was a Republican member of the House from Ohio. He was a financial conservative. He was also one of the key authors of the Civil Rights Act of 1964, with both Kennedy and Johnson saying that, without him, the act would not have been nearly as powerful.
Of course, the entire act was very unpopular with House Dixicrats, who tried every action they could to water down the act, or destroy it. For instance, one Judge Smith attempted to defeat the bill in a round about way by adding "sex" to the equation, thinking that the provision to bar discrimination of women would prove unpopular and lead to the defeat of the bill. Of course, the provision was not only added, but HELPED the cause for the act, much to Smith's chagrin. And, yes, the act did lead to a mass migration of Dixicrats from the Democrat to the Republican side.
And, honestly, that was one of the very early things which have led to the downfall of the Republican Party. Instead of being a part of fiscal conservatives, of intellects, of useful reform, the Republican party has evolved into The Part of No, a party which sometimes not-so-quietly embraces racism, reactionary, greed, wealth for a very small percent - and want by an extremely large percent, social conservative bible thumpers who are quite interested in controlling lives and attempting to ensure the dominance of their perception of the white race. After all, it is easy to scare the ignorant to believe anything as long as it is repeated enough - that the person they already think is a black muslim tree-hugging peace-loving socialist who is building towards a gunless violent police state, and whose leanings have been taught by a white hating christian preacher is out to destroy their poor white trashy world by spreading their wealth to the poor.
This party is absolutely nothing like the party of Lincoln nor McCollough nor the real Reagan. It is barely even the part of the first Bush. It is the party of Newt, Sarah, Mitt (or, at least, one of them), Michelle, Rush, Glenn, the Koch Brothers and other very rich white people. They are a very loud minority who are quickly becoming obsolete - yet would have the potential to create a danger to this country - but fortunately, there are enough people in this country to see through their little ploys, and hopefully, they will be dispensed of soon enough in a nice, quiet, electoral way.