The title seems to be a bit misleading. I haven’t seen the study this piece is based on, but given what they say here, it looks like everyone does better under a Democratic administration, not just minorities or the poor. But Republican presidencies tend to be especially bad for minorities and the poor:
Under Democratic presidents, the incomes of black families grew by an average of $895 a year, but only by $142 a year under Republicans. Across 26 years of Democratic leadership, unemployment among blacks declined by 7.9%; under 28 years of Republican presidencies, the rate increased by a net of 13.7%. Similarly, the black poverty rate fell by 23.6% under Democratic presidents and rose by 3% under Republicans.
The results for Latinos and Asians, though based on fewer years of data, show the same pattern. For example, Latino incomes grew an average of $627 a year under Democrats and fell by $197 a year under Republicans. The data similarly show that the living standards of Asian Americans have improved under Democrats and stagnated under Republicans.
More important, these gains do not come at the expense of whites. On average, white incomes have similarly grown, and white joblessness and poverty have likewise declined, under Democratic administrations. These numbers show that economic condition need not be a zero-sum game pitting races and ethnicities against one another.
First, even accounting for the overall state of the economy and other longer-term trends in well-being, partisan differences persist. When controlling for inflation and changes in the gross national product, and accounting for other factors such as oil prices and the proportion of adults in the workforce, we find similarly large gains for minorities under Democrats and equally sharp losses under Republicans.
Second, these partisan trends are remarkably consistent. Black incomes grew in 77% of the years under Democratic control, while black poverty and unemployment declined 88% and 71%, respectively. In sharp contrast, blacks lost more often than not under Republican administrations.
Finally, the longer Democratic administrations are in office, the more they appear to help blacks and other minorities experience economic gains. As Republican presidents stay in office longer, however, the fortunes of minority groups increasingly suffer.