Bill Clinton actually raised taxes on the wealthy. These were eliminated when George W. Bush cut taxes on the wealthy. The Democrats did oppose the Bush tax cuts, but the vote was 50-50 in the Senate and Cheney broke the tie. So, don’t blame Democrats for the fact Bush cut taxes on the wealthy.
Barack Obama, without a majority in Congress, was able to get a tax increase on the wealthy, but he had to agree to the sequester that froze government spending. Since government spending on social welfare programs helps the poor, cutting government spending hurts the poor. All social welfare programs since the Great Depression were enacted by Democrats and opposed by Republicans; e.g., Social Security; disability insurance; unemployment insurance; a minimum wage; Medicare; Medicaid; and the ACA.
It is true that Ronald Reagan gave us supply-side economics (cut taxes on the wealthy to stimulate the economy). What actually happened was a massive transfer of wealth from the 99% to the 1%. As Warren Buffett famously said: “It’s class warfare and my class is winning.” Democrats understand that the progressive income tax is the way to deal with wealth inequality in society. The Democrat Woodrow Wilson gave us the progressive income tax. Republicans want to cut the income tax because this will benefit the wealthy with high incomes who pay most of the income taxes.