What the data show are that the percentages of total income earned are increasing steadily for the top 20%, remaining relatively constant for the second 20%, and decreasing for the bottom 60% (Data are readily available on the Census web site). The rate of increase in real dollar income for the top few percent has been more than ten times the rate of increase for those in the middle (i.e., the middle class). For the bottom 40% there has been virtually no real growth in income over the last 15-20 years -- that is trickle down didn't trickle.
This pattern is not unique to America and, to some extent, is inherent in globalization. One of the primary effects of globalization, is inevitably that capital is more mobile than labor. I can easily unload investments in America and move my money to Asia to take advantage of lower cost labor. However, it is much harder for the labor to follow the jobs.
It is ironic that we have removed almost all barriers to the movement of goods and money, but that the movement of people is tightly controlled, creating massive economic imbalances. If, for example, cheaper labor could enter the US more readily, jobs would have been less likely to leave and our economy would be stronger. Instead, our jobs are being sold to other countries. and our workers are increasingly facing long term structural unemployment.
Neither political party is addressing this long term issue substantively. Instead, both try to cast it in ideological terms. It is really a question of economics more than politics. There is no reversal of globalization. Communication and transportation costs are less and less important to the total cost of goods. Free movement of money isn't going to stop. The rest flows inevitably.