I know it's not going to be well received by many, but this isn't the result of some specific government action or administration. As you can see, the difference between the elite wealthy and the rest spiked during Clinton's term. IMO it has a lot more to do with the fact that because of the increased sophistication and complexity of the financial system, those with great wealth have at their disposal a lot more tools to take advantage of flaws in the system than the average person. They will do better than the average person no matter which party is in power because they simply have the leverage and tools that others don't.
For example, the elite rich and power brokers were able to cash in on the dot com boom of the 90's, with inside tracks on IPO's before the "common" investor, and were then able to assume less risky positions as the dot com bubble burst. End result, they gained tremendously in wealth, while most others first gained some and then lost some.
I'm not a fan of the growing wealth disparity, I think it's a detriment to the country, but I can't think of any feasible mechanism that can be used to help bring things back into balance, short of simply stealing the money of those with wealth, which is unacceptable as well.