But let's say a country have little care to minority ethnicities. I have the many resources to arrange short benefit to them, such as occasional free dinner for those ethnicities, arranging cheap or free traveling trip for them. Essentially bribe those minorities.
Now I am elected to become a president. How do I get more resource to bribe minorities? I just receive donation from the rich and just set law to benefit them. Those law will get me donation and let the rich suck more money from the minorities. Now I have those dirty money in hand. Since minorities are living in a more challenging environment by my policy, those minorities will even more welcome my bribe and continue to vote for me.
Now you may ask, why are those minorities can't read news? Why they can't listen to the other side that may benefit to them? Firstly, minorities have very tough environment and they don't have education and even time to think about their future. Therefore, they just vote for whoever is familiar or whoever give free gifts. Secondly, a government could control the propaganda and paint those opposition as destabilizing country and blaming them as enemy and reason of their miserable situation.
It's not a hack, but a flaw. Democracy assume all people care enough about politics to understand the implication of each policy. If people don't have time resource for this, then it is pretty easy to spread propaganda to paint some enemy. People in poor condition just want to find someone to blame. And people trust the one who could bribe them a little benefit.
Of course, there are no better alternative than democracy, but people just too focus on their living and care to their own short term benefit. Long term benefit is difficult to promote since no one knows when will this be effective.