In general, this is false. Politicians generally work on the things they campaigned on, because the incentives point in that direction.
pigeon, stop being dumb. Politicians do the things they promise to do, yes, but they can also do other things they didn't promise if it doesn't contradict those promises. That's, like, politics in a nutshell.
Saying that messages need to be targeted is, like, common sense. The Democrats
need to be a party of minority issues and minority rights, yes. When they campaign in minority areas, where minorities provide the crucial votes, they need to emphasize what they do for minority issues. But when they campaign in areas where minority votes are not the crucial votes, then they don't need to. That doesn't mean they're anti-minority. It doesn't even mean that, when in office, they don't implement racial justice reforms. It just means that the emphasis of the message is elsewhere. Racial justice is still in the manifesto, it's still in the party platform, but it isn't the focus of the campaign leaflets and rallies, etc.
If you think the way to winning back Wisconsin is to turn up at the rusted out remains of the old factories and start telling cranky old white men about why they need to vote Democrat because otherwise there won't be police reform, you're going to lose. We literally just tried that, that's why Clinton lost.
And if you think you're going to get racial justice without winning over Wisconsin, you're nuts. To be President, you have to win 270 votes in the electoral college. I will always vote for racial justice unconditionally. Always have, always will. But I have the basic common sense to work out that there's not enough people like you and I to win office. That requires building a coalition - you scratch my back, I scratch yours. Cranky old white guys in Wisconsin will vote for people who assist with racial justice. We know because at least some of them voted Obama. But in return, they want people who assist with the auto industry, and so on.
That's the thing about allies, and alliances. They're not unconditional. They're mutual.