As always when questions of motivations rather than actions come up, I think we have to return to George Wallace. Even politicians who make overtly racist appeals may be much more committed to winning elections than to racism. So I'm not sure it matters much what precise mixture of partisan advantage and racism motivates Republican efforts to suppress the African-American vote; the efforts are, in the end, racist even if wholly motivated by the former. Similarly, I don't know how much racism and how much partisan advantage led to, say, Reagan kicking off his campaign in Philadelphia, MS to deliver coded appeals to southern racists (as well, of course, as the 3 Americans consistently committed to "states' rights" principles), but it's indefensible either way. Attempts to figure out whether the tunes played on Nixon's Piano are authentic expressions of subjective racist beliefs or mere self-interested cynicism are both impossible and beside the point.
As I've argued elsewhere, if the key goal of anti-racism politics is to find and punish the evil-doers who are racist, then motive becomes very important in terms of assigning culpability. But that isn't the primary agenda of anti-racism activists. We're interested in protecting those vulnerable to racist politics, and providing restitution and remedy to those who have been victimized already. In that quest, it doesn't really matter whether the motivating factor behind, say, ridiculous and unnecessary "anti-voter fraud" laws is "Black people are inferior, this will stop them from voting" (as they were originally justified in Mississippi) or "diluting turn-out among the poor and minorities helps my Party." Perhaps the adherent of the former view is a worse person than one who believes the latter; but in either case, the person for whom it is more difficult to vote is harmed in roughly the same fashion.
Most of us are willing to make the trade here. In comments to this post, I noted that I'm willing to accept higher barriers on labeling a possible perpetrator of racist activities "a racist", in recognition of the fact that intention matters for such culpability and that such charges, when false, can have serious negative repercussions. However, that concession is only a fair one when paired with a concurrent commitment to work vigorously to protect and compensate the victims of the racist activity itself. So, in the voting law cases, I'm far less interested in labeling their sponsors "racist" as I am getting the laws repealed and working so that all franchised Americans can vote unhindered and without undue delay. To a large extent, this has been the position of progressive anti-racism critics since the late 1970s, when Alan Freeman wrote his path-breaking article, "Legitimizing Racial Discrimination Through Antidiscrimination Law," [Minnesota Law Review, Vol. 62 pp. 1049-1119 (1978)]. The "perpetrator perspective" ("let's punish the evil-doers") and the "victim perspective" ("let's aid those who have been wronged") that Freeman discusses require fundamentally different outlooks. Punishing wrongdoers absolutely requires they we set up adequate procedural protection for the accused. But if the only we aid the wronged is through punishing the wrongdoers, then we're resigned to the fact that many victims won't gain redress at all. Sometimes, there isn't enough evidence to convict even when we know someone has been wronged. Other times, a procedural technicality lets the known guilty go free. In racism cases, especially, it can be difficult if not impossible to identify a discrete "perpetrator" whose "responsible" for the harm at issue (who is responsible for the "Blacks as bestial savages" meme which infects so much of the White psyche on crime issues today?). Organizing anti-racism politics in this fashion is wildly one-sided against the victims.
The better alternative is to offer redress to victims independent of punishing perpetrators. Victims of robbery should be compensated regardless of whether we can criminally convict the robber. It would be morally shocking if, in absence of such a conviction, we then denied that the victim had undergone any colorable moral wrong. Victims of racism should be accorded the same treatment, compensated regardless of whether we can convict "the racist" to blame for it.