Households earning over $10 million have a much lower effective tax rate than households with incomes between $500,000 and $10 million. That is because Reagan and Bush reduced the tax rates on investment income. Those with incomes over $10 million receive much of the their income in dividends and capital gains which are taxed at a lower rate than income earned from wages. Tax policy in the US has been modified by Congress to favor rentiers. There is no evidence that taxing investment income at lower rates than earned income benefits anyone but the rentiers.
The majority of Americans have their investments in tax deferred retirement funds. They pay no taxes on capital gains and dividends until they begin to draw their money out of those accounts. It is taxed as ordinary income when it is received in retirement.
The Obama Administration made modest changes in tax policy to fund the Affordable Care Act. Those changes will primarily affect the super rich who get the lion's share of dividend income and capital gains. It is not surprising that Republicans oppose the Affordable Care Act. The super rich are forced to help pay for the healthcare of people with whom they have no social contact. There are not enough super rich voters to influence elections in the US. They depend upon the politicians, whose campaigns they fund, to whip up opposition to policies that they do not like. They are good at convincing lower income voters that policies designed to benefit them are bad policies.