Is the U.S. income gap holding back economy?

Yes, it is; Reestablish a U.S. manufacturing foundation (sell the merchandise at a reasonable price so the world will buy it), and the middle-class income gap will start to disappear. So they can start to generate revenue for Washington DC to waste on crony's. The way it is right now the middle class they are juggling every penny to make ends meet. The middle class going out and buying stuff because they wanted it - it is not going to happen. There are going to be a lot of U.S. retailers go out of business in 2014 making the income gap even larger. Because of this circle that needs to be broken.

The wording of the question leads me to respond with "the gap itself isn't an issue". I don't consider an income gap to be inherently bad, but I think the various nuances that accompany our existing income gap are bad.

Our political policies and tax rates are actively encouraging the income gap to grow, and harming quality of life for a large portion of Americans. If we agree that we want to tax income, then we cannot create and maintain policies that allow a higher income individual to pay a lower portion of their income in tax. That's just the basics.

When healthcare, SNAP and social security find themselves on the chopping block, lower income brackets find themselves riddled with risks and decrease consumption of staple goods (thus harming the production and profitability of staple goods). The political engine that is funneling money from the lower income brackets towards the higher ones is holding back the economy.

The "income gap" is a problem only because people are told it is. It's a purely perception based issue. The disparity between rich and poor in the US is growing, yes, but the quality of life at all levels is also growing, even the lowest. The gap has been going only because the rich have been getting richer faster than the other groups. This does not mean that the other groups have been getting poorer, or declining in standard of living. Quite the contrary, the standard of living has been continuously increasing everywhere.

This is where the marxist inspired economic egalitarianism falls apart. It assumes a 0-sum economic game where one must inherently loose for another to win. Historically, though. industrialization and profit-seeking scientific advancements have allowed all participants to benefit from trade, even if some benefit more than others.

If we stop worrying about the other guy's glass being overflowing, we'd notice ours has been filling up too.

I think too much emphasis is being placed on the income gap WITHIN America, and not enough on the income gap between America and the rest of the world. The same people who decry "corporate greed" will also complain about off-shoring jobs to 2nd-3rd world countries who desperately need to raise their standard of living to at least a level we would consider lower class here in the USA.